There are many different ways that my students can earn money: classroom jobs, completing their homework, retaking quizzes and improving their score, participating in class, turning in exceptional work, etc. In turn, the students can save up their money and use it on a number of different things: $2 for a hallway pass, $20 for a no-homework pass, $2 for getting a copy of a lost assignment, $5 for borrowing the teachers supplies, $6 for classroom candy, etc. I also have a Wheel of Fortune Wheel and a Plinko board. Students can pay $25 to spin the wheel. On the wheel they can lose money (get anywhere from $20-$1 back or even go bankrupt) or they can win big time (earn $40-$100 back or even get a jackpot which is an envelop that holds all of the money that past students lost on previous spins). As for my Plinko board, students only pay $10 to play and they can earn smaller prizes depending on where the chip lands.
This system has been so successful in helping to keep the students prepared. I found that many of the students who regularly didn't complete their homework assignments started to come to class with it all finished just so that they can earn money. I also had an increase in the number of students that came before and after school to retake their quizzes.