I hate Delrin. Makes an awful sound rattling against metal objects. Originally, I got a few and still use MTM 50 ammo boxes. They work fine, but cells rattle a little against the plastic. After refreshing my 5yo Eneloops, I wanted something to treat my new cells a little better, and I got a Comcase Battery Organizer, which has nice snug holes in foam to prevent any cell rattle. I wanted a separate case for my 14500, so I also got the Malamute Rugged Battery Organizer, and I am very satisfied. The base of the Malamute is more like rubber than hard plastic, so the cells rattle ever so slightly, but against the tacky rubber-like material it makes it a non-issue in travel.
If you need to carry only one spare AA cell, just get a small AA flashlight and carry your spare cell in there.