DJ,
Last year for spirit they had you prepare a piece (I used an Arban Characteristic Study). they also had a few exercises to perform and i THINK i played a chromatic scale?
At Cavies auditions we had/have a whole packet of information and exercises, as well as a few pieces.
I would suggest checking the websites of the corps. At any camp, be prepared to do anything you would at a normal rehearsal. Spirit had us running and prepping for pretour at the audition, while cavies did NOT, so the actual process will vary by corps.
Hope this helps, and feel fre to msg me if you have other questions.