Well, this is not an upcycle project, but one of my students was carrying a backpack with zipper totally broken, so it was always open.  I offered to give him a new one since I had 3 backpacks I was going to sell at our garage sale, but he didn’t want a new one.  He is really attached to it.  So I offered to fix the zipper.  It looked relatively easy.
Before:

Afater:

I could not find gray zipper, but he was very happy to see the backpack with a working zipper.  He is excited that he can put stuff in it now.  It was great to see his smile. 🙂