You can do a lot around the house. If your parents won't pay you for chores then you can go out and help out with people your parents know. Like mowing lawns. Washing windows/cars. Give baths to friends pets. Walk pets. Pull weeds. Just have to think about all those things that us adults don't like to do on our own (: haha or like they said above, just sell some things you don't want anymore.
If you're a kid go to your neighbors and ask them for work. Wash cars, mow lawns, do gardening work. Do a very good job for every one and they will always call you back to do more work! Also be nice and polite.