This is Vaughn's Rock Star Jar:
When he does his chores, or I notice him doing something especially nice, then he gets to go out in the backyard and pick out a rock to put in his jar.
When his Rock Star Jar is brimming with stones, he gets one dollar and gets to pick out anything he would like from the dollar store.
If there is a good sale or something at the store that I really want to get him, then I buy it and save it in my "store," which gladly accepts Vaughn's hard earned dollars too.
I got the idea from my friend in Michigan who has four boys. They each have a jar and it works well for her. Only I think she uses marbles, but I was too cheap to go buy marbles so Vaughn gets Rocks from the backyard instead.
It's amazing what a little guy won't do for a rock and a dollar bill.