From the Kickstarter campaign:
These coasters will have printing on both sides. The back side will just feature the DrunkQuest logo. But the opposite side will feature a unique game rule. These rules will always benefit the player in possession of the coaster. The coasters should be given to the players at random at the beginning of the game. When a player finishes their drink during the game they can flip over their coaster to reveal its reward.
- DrunkQuest: Drink Coasters