I'd seen elastic boards like this, made commercially, and thought they'd probably be reasonably easy to make. Now DesignSponge has a great tutorial. Need to make one (or more) of these for Mr. M for Christmas.
DIY Swiss Army Key Ring from DIY Hacks and How Tos on Instructables here. There is a video tutorial and a written tutorial and the supplies needed are really cheap. GIF by me using from DIY Hacks and How Tos’ tutorial.