Today I made a little carry system for my ski helmet on my ski pack. It’s very simple, using lightweight ripstop nylon, about 4 feet of shock cord, and a cord lock. It mounts to the 4 side compression straps of the pack, and is pretty quick and easy to insert and remove the helmet from.
I wish I’d used heavier fabric, as the very thin ripstop I used was a pain to work with and some of my seams came out ugly. This is also probably a good project to use some stretchier fabric for, but I didn’t have any lying around.