Monopods are cool. A little bit of camera support when you need it, without having to carry around a clunky, three-legged thing. I have a few.
In my search to find small and light stuff, I ran into the Manfrotto 790B. It's particularly cool because it folds up to 15 inches in length -- but expands to be just fine for a six-foot tall photographer. Really lightweight, and well-made.
Don't put a huge camera with long glass on top of it. But if you need something to hold up a small DSLR and a reasonable lens, it's worth trying. I've been using one for a while, but I'm posting now because I noticed these have dropped to about half price.... Not a bad addition to a small photo backpack.