I'm in the process of doing the same thing, practicing all summer to audition for a jazz band in the fall.
First you have to know what kind of band you're auditioning for. The ones that I'm auditioning for are primarily big bands, so what I'm focusing on is getting the basics down then moving on to big band specific technique. Another thing you need to know is how the audition is structured. The big bands I'm auditioning for place heavy emphasis on sight reading, so I'm centering a lot of my summer practice around building up my sight reading skills. If yours is more focused around repertoire, then I'd say start memorizing changes for as many standards as possible, especially ones that you think they'll focus on.
All in all, a good idea is to just get some CDs, get a real book, and start walking through as much as you can. If you can get fairly proficient at that, then I'm sure you've got a chance at the audition.
Personally, I've been getting A LOT of books.