Dojo Reward Coupons

I use these for my kids to cash in their Dojo points. You can use them however you please, but... how do I do it? I print these on colored paper, using different colors for different ranges of points (blues for 10 to 20 points, pinks for 21 to 30 points, etc), then I cut and laminate them. At the end of each week, the kids choose the coupons they want according to how many points they have and they then get a chance to use the ones they've got (I reset points the 1st of every month).

At the begginning of each year I ask my class what prizes they would like and I add them to thiese if I find them reasonable, so they will be updated.