When kids are following the rules, or are a volunteer for something, they get a chance to pick a number. If the number they choose has a post-it note on the back, they get what the note says. The next time I use this method, I plan to include bad prizes too, such as a pie in the face, or a bucket of slime poured on them etc. Wheel of Destiny I've heard of other groups using this idea, and I think it's good too, although I haven't gotten around to making one yet. Make a wheel out of wood.
Kids spin the wheel.
The sections on the wheel are both good, and bad. They could include 10 Wise Buy Bucks, Candy, Prize, Pie in the Face, etc. This method can be used along with a prize method. This idea is used more to keep the noise level down, when kids get a little loud, as a group. Put 3 red balllons taped to the back of a chair, or a pole, or whatever, on the girls side at the front.