The “string tripod,” as seen below, is most likely the most portable camera holding solution you’ll see here. This “tripod,” as seen on Instructables, it is literally just a piece of string attached to a 1/4 – 20 eyebolt. The bolt is screwed into the camera, then locked down with the corresponding nut.
When you step on the bottom of this string, it allows you to put tension on it with your camera, stabilizing the shot. I’d recommend putting a surgeon’s loop knot on the bottom for an easy foothold.
A quick search of Amazon reveals an interesting take on this, an attachment that goes on your belt loop. This could also be a DIY job, possibly with some sort of blunt hook.
Matt Heilman of shared his smartphone string tripod today via Google+. I didn’t think this “tripod” could get much simpler, but with a smartphone’s offset camera, all that’s required is to tie a piece of string around the body, and one around your foot.