Well I went to the gym today, did a leg workout/stretch, then I got some 70lb DB's and walked around the gyms little track. I made it halfway, dropped them, picked up and went almost the other half, dropped, then picked up again and finished. I don't know if it's working my grip, but it sure as hell is working those forearms. I then picked them up again and just held them for 20 seconds, which was really how long I could hold them in a decent manner.
This is called a farmer's walk, I found it on some site when searching for grip techniques. Pretty much the only thing I can do are these. I can hang from the chin up bar, I'm about 295lb, so I don't really get a use out of that exercise, and the gym doesn't have wide bars that I was reading about, something like 2 inches thick.