diesel...i agree. unless it's a "party" for 5, a 30-pack will last like 30 minutes. Woooohooooo!!!
Seriously. If you're going to have any sort of decent size party, you'll need any of these. Or all if you want a huge bash.
Kegs. Yes, plural.
Several 30-packs. You'd be amazed how many cans you can toss into a bathtub of ice. Tubs hold a LOT of beer

Mixers. People love their margaritas, rum and cokes, screwdrivers, etc.
A large container of Jungle Juice.
Wine coolers, Mike's Hard, Bacardi Raz, Smirnoff Twist type drinks for your lady guests. Not all girls want to drink cheap beer all night. They may be considered "B***h beers" and a lot of guys won't touch them, but it'll go over well with the girls.
If I'm forgetting something, I'm sure others will fill in.