Disassemble old computers and sell the parts on eBay
Walk the dogs of elderly people in your neighborhood.
Run errands for elderly people, get their trust by doing good work quickly.
Not too many things you can do, because of the child labor laws (if you are in the USA).
Do computer chores, like typing or retyping documents, cleaning out spyware and viruses. Learn design and photo editing so you can help people who need it done but do not have the time. Begin designing simple web sites. Learn how to setup accounts, and update web pages.
Clean computers by using Queue Tips, Alcohol, and Dust off.