I walk a lot, too. It really helps me think and get away from the usual triggers. Stay healthy and don't forget to eat!
Maybe you can find other ways to fill those walking hours. You can make a destination to walk to (the park or something) and then spend your time there journaling or drawing. You can also see what curiosity shops are around your area and go exploring! Or go to the library and discover random facts.
If you have a lot of time on your hands you could see what volunteer work is available in your area and get involved that way. Helping other people is a great way to keep your mind off yourself and any triggers.

The suggestion for wood-burning is great and I totally agree! You could also try the rubber-band snapping, although I've noticed it does leave welts if I do it excessively. There's less overall damage, though.