I have over 1000 students who I teach and wanted to give them candy. So in the last 5 minutes of class they were able to pull from a hat a card. If they pulled the trick card, no candy, if they pulled the treat card, the could choose a candy. Each class has about 40 students so i printed 34 tricks and 6 treats.
Very simple, but students were excited when they learned they were going to be treated at the end of the class.