In this instructable you'll see how much easy is to build your own bike fender with reused plastic stuff. This is not only fun and cheap, but it also will convert at once a garbage into a plastic gadget ready to use, and this is the best way to recycle.
Step 1: The garbage
Cut the rounded part with the scissors and refine the border with a cutter, beware to not cut yourself! You'll obtain a boat shape, leave some plastic on the corners of the back sides, so that they will help to reinforce the connection with the frame.