Loose change; loose hardware like nuts and bolts and hinges and nails; punch holes in the bottom and use top and bottom for starter planters for low-intensity gardening, as in starting a sprinkling of heritage tomato seeds in one, various flower seeds from dead-heading plants in another, etc. As planters these need to stand in a low waterproof flat to catch the run-off. Kids love these for stamps, cutouts, and other treasures. They rust, so just recycle. Many, many other uses.