Headbands, hair clips, little gymnast survival kits, blankets, meet-specific souvenirs like a shirt or cup or other memorabilia, fun socks, key chains, photo frames, lip gloss/chapstick/lotion. Last meet, my DD went nuts for pencils that said "gymnast". One big item I've thought would be nice to see for sale are cushions/stadium seats for the lovely bleachers.
Items suggested above like organic soaps, scarves, etc... While these are things I like and would not mind seeing for sale, I am personally in kid mode when I am at meets, so I'm not super certain that I'd personally buy those things. Granted, maybe it's totally just me.

All of my allotted spending cash ends up going to the kids at meets, and they like the "crap", the raffle, and snacks. And my DD always, always leo shops. So I don't know that I'd nix those things completely.