After we each have collected 10 gold stars (for each day of running), we get to buy a box of ice cream sandwiches. And can't buy any until we've each gone running 10 times. (That's the hard part.)
Now we just have to come up with bigger prizes, for when we've kept up running for a longer time. And the place where we keep our gold stars has to be portable, so that we can take it with us to Saskatchewan for the summer.