Environmentally Friendly Arts and Crafts?

I'm doing volunteer work at a summer camp, and I would like to design an Arts and Crafts activity for my campers, but am out of ideas. They are 5-7 years old, and the camp is all about using minimal waste, or reusing. This weeks theme is Time Travel so if it could be something related to that it would be PERFECT. but if not I'll make due. Any Ideas? Thank you.