Introduction: Keep Your Zipper Up: It's Easy As 1, 2, 3
Step 1: Get a penny-sized key ring. The size has to be just right to cover the zipper head and the button area. It can't be too large as it will not be able to restrain the zipper from falling.
Step 2: Put the ring in the zipper's head.
Step 3: Hook the ring in the zipper's head to the button and close the button. Voila.
No ring? No problem. If you can't find a ring, you can use a paper clip and make one instead. Another good alternative for the ring is the twist wire. You know, the strip of wire you always find in your electronic gadget cables.