This is a quick fix you can use on all your camping gear.
1. Identify which side of the zipper has the box (Left side in photo) and which has the pin (Right side in photo). The zipper slider needs to be replaced on the side with the box:
2. Find the plastic stop at the top of the side with the box:
3. Using pliers, carefully remove the plastic stop. A small hole is usually left, but try not to damage the zipper tape more than necessary:
4. Line up the slider so the zipper coil will face towards the angled side of the back of the slider, and insert zipper coil into slider:
5. At this point, the zipper will function as normal- the zipper stop on the opposite side will stop the slider from coming off when both sides are zipped together, although the slider will come off when pulled to the top by itself. It can then be replaced just as easily:
6. If you want to add a stop at the top end of the zipper, you can create one by stitching over the top of the zipper coil (pictured) or purchase a zipper repair kit which will have small metal crimps you can place at the top of the zipper: