Rubber bands, a variety of empty containers
Collect a variety of rubber bands, big and small, thin and wide. Then use all different kinds of containers to stretch the rubber bands around to make a musical instrument. You can use anything from a Tupperware container to a yogurt or pudding cup, even a styrofoam container that your mushrooms came in. If rubber bands can be stretched around it, the opening can make music when you strum the strings. Let the kids try all different kinds of containers to see how they make different sounds.