Here's a handy technique I'd like to try next time I'm in the woods: Measure Distance with a standard Compass.
By using two known angles, and a reference distance, you're just a little trigonometry away from knowing how far away a point is. Or, more succinctly:
distance = (Tan (90 - (A -B))) x Ref
Finally, a reason to carry my cell phone (which has a calculator on it) when I go on a hike.