I just took a class last week where the teacher used this in her classroom. She teaches junior high and high school SS, economics, and geography. This is how she does it:
1 ticket= A on a homework assignment, extra credit, etc.
2 tickets= A on a quiz, Student of the week, good responses in class, etc.
3 tickets= A on a test, extra project done(like map making), etc.
Then she had a time before class and after class where you could purchase stuff. She had a set list for how many tokens it would take:
notebook paper, pencil, pen, = 1 ticket
gel pen, Tootsie Pop= 2 tickets
candy bar, free assignment, =5 tickets
deliver a flower or plant to someone = 50 tickets
supper with her= 50 tickets
There were lots more prizes, but this is all I can remember right now.