Crafty people seem to be able to make works of art out of other people's trash with little or no effort. If you need some ideas or directions, hundreds of Web sites detail thousands of homemade art possibilities, and many of these projects list cardboard as one of the primary building materials. Family Fun provides directions on building superstructures such as cardboard barns, skyscrapers and the like. Other rainy-day ideas include cardboard costumes (such as chicken and washing machine designs), sandals, spy periscopes, guitars and more. You can find plenty of Web sites that offer instructions on building cardboard trucks, trains, robots and TV sets. The only supplies you'll need are plenty of cardboard and some everyday items you're bound to have lying around the house.