When I was staying at a friends dorm back in '99 we got so hard up for tobacco once we went out and walked the campus, picking up every butt we found. We broke them all open into a tray back at his dorm and then rolled the old tobacco mixture up with cheap zig-zags. Nasty stuff, but we were young and full of stupid.
Being an outdoorsy kinda guy, I've also smoked Acorns. I know it sounds weird, but it was actually a very good smoke and had a very calming effect to the smoke. Now that I think of it, it was probably one of the best smokes I've had. (I should note, this was out of a clay "peace-pipe")