I have a sort of mini career fair at my internship tomorrow. I work at a University Affiliated Research Facility. Any tips for talking to job reps?

show personal interest in the person who is offering jobs. Give compliments about cloathing etc. And remember you don't beg for a job you have something to sell they need. But you have to be very clear what benefits you offer for them.
Do you have a cool side project you can show?

Show genuine interest and ask lots of questions. Boosts up your knowledge of the job and let's them know that you have the ability to do some thinking about stuff related to the job.