positive reinforcement (no treasure box!) I do something like this in my classroom and it is AMAZING how motivated the kids are to earn the "coupons" from "Mrs. Fuller's Coupon Box." Top pick by 2nd graders, "lunch with the teacher." Just a warning, if you don't want to eat lunch with your students a couple times a week, don't give that as an option! haha.
About once a month, choose a student to receive the "positive postcard". Actually mail a postcard to their house! They love receiving mail from their teacher. Their parents especially love it...it's sure nice to know that their child is succeeding.