Designate someone to be the “Guru” (or master, or superstar, whatever name you like best), personally I think it works best when the Guru is an adult leader. Then take volunteers of challengers who will attempt to “beat the guru” and some minor tasks (stand on one foot the longest, trashketball, catch more popcorns in your mouth, tic tac toe on the marker board, etc). If they can beat the guru in the task, then can win a little treat.
A variation: Beat the Guru: Casino Style
Same game as above, except give each student a cup or baggie of M&M’s or Skittles, and before they challenge the guru, make them make a wager of candies. If they bet 5 candies and they win, they get 5 more. If they lose, they must pay up!