Keep it simple - do some PP if you'd like, even a couple butts should be sufficient. After that, I'd tend to stay away from larger hunks of meat, as you run the risk of letting things get pretty expensive, with some cooking space issues to boot.
Here's a couple other ideas that I've used at my own place that have usually worked well:
- Plain ol' hot dogs - everyone loves a good hot dog, easy to make, grill them to keep the smoker free.
- Chicken wings - fairly cheap, but consistant and easy to make, grill them to keep the smoker free.
- Meatloaf - fairly inexpensive, can be premade. Make it the day before, refridgerate, slice cold and grill up for sandwiches. Nice break from the normal hockey-puck hamburgers.
- Chili - you said a tailgate, right? Brew up a pot of chili, and have some of the other folks agree to make some as well, so there's a couple different kinds to choose from. Everyone has a favorite chili recipe.
- Nacho Bar - This one can consist of anything, can go hand-in-hand with the chili, easy to re-stock and replenish without the risk of a lot of waste.
If I told people what I use to cook, they probably wouldn't want to eat my food...