It's an excuse to play a bunch of mini-games: jousting, wrestling, racing, etc. Maintaining your disguise, cheating, and foiling the other team's attempts to cheat are unofficial but vital events.
One of the events is Potion-Quaffing. It's pretty straightforward: a Whitehack-style blackjack roll based on Constitution, and a random table to come up with really awful potions.
Think you could stomach some Nectar of Curdled Frog Gall with a Slice of Sea Cucumber?
How about a tall glass of Hag Wart and Heartache, Haunted by a Vengeful Ghost?
Maybe Pearls of Sugared Shoggoth Wool and Runny Cheese, on the Rocks, Served in a Pumpkin Shell?