Lens caps have an almost supernatural ability to go missing, and without that slender piece of plastic, you're constantly worried about the condition of your glass. Now Mark Stevenson, an engineer from Chicago, has put together a kickstarter project to fund what he's calling the "Camera Lens Cap Holder." This double sided plastic doodad would slide through your camera or bag's strap, and would give you a handy place to stow your lens when shooting. It will only hold one cap at a time, but it would be an extremely quick and easy way to put your lens cap somewhere secure — as opposed to pocketing it, which is what I generally do.
The current prototype of the holder will be able to handle 3-4 lens cap sizes. Here are the configurations in the works:
52mm, 55mm, 72mm & 77mm for Nikon, Pentax, Fujifilm, Sony, Pro-series and vintage lenses
46mm, 58mm & 67mm for M4/3, Cannon (sic) and Nikon lenses
40.5mm, 49mm & 62mm for M4/3, Olympus and vintage lenses
If you decide to help fund the project, it's only $15 to get one sent to you as soon as they're made. The only immediate problem I can see with this idea is the trouble of reversing it if you want access to the other side. I honestly can't imagine unthreading my camera's strap in order to flip over the cap holder.