What ideas do you use to get borrowed items returned?

I always had lots of pens/pencils to loan the students that didnt seem to come prepared to class. So often, the loaned pens/pencils never seemed to return at the end of class and the supply would quickly dwindle. Eventually, I started the idea that if you wanted to borrow a pen/pencil from my desk, you had to give me a shoe....when they returned the borrowed item, the shoe was returned. It was something they always remembered to return to me.
What other ways do you use to get loaned materials back?
Gail Hennessey
http://www.gailhennessey