Any tabletop gamer will turn trash into terrain. People have been known to make a whole town out of cardboard-there are so many types, brown paper bags and you name it-it sounds odd but any hobby store will know a group. Styrofoam esp is something they use-if you have some from inside packages-they will use it and this is something that just sits in a landfill.
www.gamesworkshop.com can give you ideas. It sounds odd but some of the things I've seen-you'd never know what it was made of because of the combination of glue paint and other assorted items brings new life to whatever it is. There are other sites not sure where-lookout hobby terrain making of and you'll prob get quite a few sites.