Glasperlenspieler

Another good question for grad students: What do you do in your spare time?
While it be nice to know what extracurricular activities are available in the are, the real importance of this question is in seeing how they react to being asked about their spare time. That will tell you a lot about quality of life as a grad student in the department.
Also good to ask questions that get at departmental politics, especially if you can do this not in writing. Who do you have on your committee and why? Who would you not put on a committee together? What are the factions/fault-lines in the department?

Another good question for grad students: What do you do in your spare time?
While it be nice to know what extracurricular activities are available in the are, the real importance of this question is in seeing how they react to being asked about their spare time. That will tell you a lot about quality of life as a grad student in the department.
Also good to ask questions that get at departmental politics, especially if you can do this not in writing. Who do you have on your committee and why? Who would you not put on a committee together? What are the factions/fault-lines in the department?

I wouldn't put too much stock in that. Being a potential student is sort of awkward as it is and especially in this scenario, so you probably didn't really have a chance to see their personalities. Plus, you don't even know which of them will end up matriculating. I would try to talk with current grad students (preferably out of earshot of faculty). Their personality/behavior/attitude will be much more telling.

I wish I could speak this confidently about articles I've published in high quality journals.

Will you have the opportunity to pursue your interests in an academically stimulating environemnt? Yes
Will you benefit from high quality advising? Depends on who you work with
Is it worth spending 60k plus cost of living so that you can do those things and maybe (but maybe not) have a more successful PhD application next time around? No way in hell

Will you have the opportunity to pursue your interests in an academically stimulating environemnt? Yes
Will you benefit from high quality advising? Depends on who you work with
Is it worth spending 60k plus cost of living so that you can do those things and maybe (but maybe not) have a more successful PhD application next time around? No way in hell

While there's a lot of truth in this, it's also worth noting that there are some veterans on this forum who are well into their PhDs or finished with them and can certainly provide some valuable insight into academic life. Among them are @Ramus, @Warelin, and @Bumblebea. (I don't want to so presumptuous as to place myself in this esteemed crowd, but I've also been around for bit, having just passed my qualifying exams). You should certainly take all advice with a grain of salt. This is especially true of anonymous advice, though as @Ramus rightly points out, even your professors aren't immune to giving bad advice. However, it's also important not to merely accept or reject advice on the basis of whether or not it's what you want to hear.
NB: none of this is to deny that it's a very good idea to reach out to people who may have more direct insight on your particular situation and see what they have to say.

I wish I could speak this confidently about articles I've published in high quality journals.

I wish I could speak this confidently about articles I've published in high quality journals.

I wish I could speak this confidently about articles I've published in high quality journals.

I wish I could speak this confidently about articles I've published in high quality journals.

I wish I could speak this confidently about articles I've published in high quality journals.

I wish I could speak this confidently about articles I've published in high quality journals.

I wish I could speak this confidently about articles I've published in high quality journals.

I understand that you're nervous about admissions, but posting this in all the threads is not the way to go. It distracts from the ongoing conversations.

I'd echo @snorkles but also add that you should remember that at this stage of the game, you are evaluating them. They've already accepted you and decided they want you to come (barring some unlikely horror story). So you're job now is to figure out if you like them. So, be yourself, ask questions, and keep your eyes open for signs (good and bad).

1. Save up money. Moving to a new city and starting grad school can have lots of unexpected financial costs and you might not get your first paycheck until a month or two into the program. It's also good to figure out housing, home essentials you will need to buy, etc. as early as possible. There will be a lot hitting you once you move, so the better prepared you are, the less stressful it will be.
2. Read something that has nothing to do with your research, hang out with friends, binge watch a series, get some R&R. You will want to be fully energized at the start of grad school. You're bound to feel burnt out at some point, but preventing that from happening too early will make your first year much more pleasant.
3. If you must do something academically related, then try to read a few things for your classes in the first semester. Ideally, try to read things that will be assigned for the middle or the end of the semester. You'll probably keep up fine for the first few weeks, but you're bound to get bogged down at some point, so having that big book that you know you will have to read out of the way will give you a little breathing room down the line. If you do this, take good notes though, so that you don't forget everything you have to say about it by the time you need to talk about it in seminar.
 

1. Save up money. Moving to a new city and starting grad school can have lots of unexpected financial costs and you might not get your first paycheck until a month or two into the program. It's also good to figure out housing, home essentials you will need to buy, etc. as early as possible. There will be a lot hitting you once you move, so the better prepared you are, the less stressful it will be.
2. Read something that has nothing to do with your research, hang out with friends, binge watch a series, get some R&R. You will want to be fully energized at the start of grad school. You're bound to feel burnt out at some point, but preventing that from happening too early will make your first year much more pleasant.
3. If you must do something academically related, then try to read a few things for your classes in the first semester. Ideally, try to read things that will be assigned for the middle or the end of the semester. You'll probably keep up fine for the first few weeks, but you're bound to get bogged down at some point, so having that big book that you know you will have to read out of the way will give you a little breathing room down the line. If you do this, take good notes though, so that you don't forget everything you have to say about it by the time you need to talk about it in seminar.
 

1. Save up money. Moving to a new city and starting grad school can have lots of unexpected financial costs and you might not get your first paycheck until a month or two into the program. It's also good to figure out housing, home essentials you will need to buy, etc. as early as possible. There will be a lot hitting you once you move, so the better prepared you are, the less stressful it will be.
2. Read something that has nothing to do with your research, hang out with friends, binge watch a series, get some R&R. You will want to be fully energized at the start of grad school. You're bound to feel burnt out at some point, but preventing that from happening too early will make your first year much more pleasant.
3. If you must do something academically related, then try to read a few things for your classes in the first semester. Ideally, try to read things that will be assigned for the middle or the end of the semester. You'll probably keep up fine for the first few weeks, but you're bound to get bogged down at some point, so having that big book that you know you will have to read out of the way will give you a little breathing room down the line. If you do this, take good notes though, so that you don't forget everything you have to say about it by the time you need to talk about it in seminar.
 

1. Save up money. Moving to a new city and starting grad school can have lots of unexpected financial costs and you might not get your first paycheck until a month or two into the program. It's also good to figure out housing, home essentials you will need to buy, etc. as early as possible. There will be a lot hitting you once you move, so the better prepared you are, the less stressful it will be.
2. Read something that has nothing to do with your research, hang out with friends, binge watch a series, get some R&R. You will want to be fully energized at the start of grad school. You're bound to feel burnt out at some point, but preventing that from happening too early will make your first year much more pleasant.
3. If you must do something academically related, then try to read a few things for your classes in the first semester. Ideally, try to read things that will be assigned for the middle or the end of the semester. You'll probably keep up fine for the first few weeks, but you're bound to get bogged down at some point, so having that big book that you know you will have to read out of the way will give you a little breathing room down the line. If you do this, take good notes though, so that you don't forget everything you have to say about it by the time you need to talk about it in seminar.
 

This is a really important observation.
 
I'll just add to the sage advice offered by @BwO, @EM51413, and @WildeThing and say that before attending an interdisciplinary or comp lit program, it's certainly a good idea to look very closely at their placement record and I would also advise taking some time to look through what sort of jobs get posted here: https://academicjobs.wikia.org/wiki/Academic_Jobs_Wiki
It's true that one can't predict the market 5-10 years out, but I also think the volatility in desired specialties is just as likely to mean that the market for a given specialty will get worse as it is to indicate that there may be an increased demand for a particular specialty. 

This is a really important observation.
 
I'll just add to the sage advice offered by @BwO, @EM51413, and @WildeThing and say that before attending an interdisciplinary or comp lit program, it's certainly a good idea to look very closely at their placement record and I would also advise taking some time to look through what sort of jobs get posted here: https://academicjobs.wikia.org/wiki/Academic_Jobs_Wiki
It's true that one can't predict the market 5-10 years out, but I also think the volatility in desired specialties is just as likely to mean that the market for a given specialty will get worse as it is to indicate that there may be an increased demand for a particular specialty. 

Also, as a general piece of advice, you might want to apply to some MA programs first. It sounds like you're still in the process of totally figuring out what you want to specialize in, and MA programs are great for that, since you get some more time to develop the depth, etc. that you say you feel like you're currently lacking. Good luck!

At the point, the best thing for you to do is gather as much information about the program as possible so that if you are eventually offered a spot (which may happen at the last moment), you will be prepared to give an informed answer.
Asking questions about the program will also demonstrate your interest, which could help you, though I think at this point there's not much you can do to improve your chances of admission. They obviously like you, otherwise they wouldn't have put you on the waitlist. What you need to happen now is for enough people to reject their offer (and depending on how they manage waitlists, people in your field). But you demonstrating your further accomplishments won't help that happen.

At the point, the best thing for you to do is gather as much information about the program as possible so that if you are eventually offered a spot (which may happen at the last moment), you will be prepared to give an informed answer.
Asking questions about the program will also demonstrate your interest, which could help you, though I think at this point there's not much you can do to improve your chances of admission. They obviously like you, otherwise they wouldn't have put you on the waitlist. What you need to happen now is for enough people to reject their offer (and depending on how they manage waitlists, people in your field). But you demonstrating your further accomplishments won't help that happen.