Punching bags are good, but I have this MUP around here that is lightly used and I just go and relax - nothing to worry about except maybe the occasional deer, tortoise, or rabbit. I love it because it is in the middle of nowhere so it kind of combines the nature feel of trail riding, but I can relax, sometimes I can close my eyes for a bit.
Other than that, I find trail riding, commuting, actual "road" riding to be somewhat stressful.