In my lab, we have opportunities for both paid and volunteer RAs to contribute to publications and presentations, with the caveat that it must be done outside of their usual hours in the lab. Thus, if they have committed to volunteer 20 hours a week for the lab and would like to be a part of an upcoming publication or presentation, they are expected to make extra time in their schedule to work on these opportunities. Similarly, if a volunteer (undergrad or grad student) desires to submit a poster for a conference using our data sets, they must conceive of the idea and do considerable background research far in advance (months) of the abstract deadline, as hastily contrived research ideas do nothing to improve the stature of our lab or our PI.
Edited to add: This is the same for paid employees. For example, I work 40+ hours a week for the lab, but then must put in hours on my own time to be included on the presentations and papers I have been on.
Basically, the opportunities exist, but must be worked for and earned and are not just handed out for meeting expectations regarding assigned tasks.