The keg in the party scene was real, filled with Miller High Life, and was used to "pay" the extras in the scene.
Most of the extras in the party scene were actually a bit inebriated when filming the party scene, as the production was substantially delayed due to the fact that the film stock was accidentally locked into the school location that was used earlier in the day, and while they waited for it to be returned, the extras had little to do at the party location but drink free beer and watch college football.
To maintain the distance between Michael (Justin Baron Sample) and his estranged father, Arthur, Jack O'Donnell was not brought in to the table read, and neither actor was allowed to talk to one another until they ran their lines in the on-set rehearsal.