Current undergrad seniors applying, I feel your anxiety about leaving school. I really couldn't envision myself doing anything else but took a couple of years to do other things because every single mentor told me it was a good idea.
I started applying to on-campus administrative jobs (in the English department, libraries, stuff like that) shortly after graduating and struck out after about 20 of those (maybe about 6 weeks in application time). I ended up getting an entry level customer service job and it's been pretty wonderful. If you end up in a similar situation (I hope you get in, of course), I think you'll find that it can be really nice to watch and read literally anything you want. Especially if you can manage to stay in the town where you went to school and can remain connected with your mentors. I pretty much only spend money on food, rent, used books, and criterion collection flash sales, so I've also been able to build up a little nest egg to help pay for living expenses when I'm (hopefully) living on a stipend next year. :]
I'd say don't worry too much about lining up other plans until you know for sure that you'll need to find a job. Employers don't really hire more than a month or two out anyway, and because you're strong writers/communicators you'll have an easy time of it.