I just remembered a navigation technique we learned during SERE training in the military which I'd like to share.
If you want to keep a straight course when visibility is low, then you can hold a 3-5m long "stick" in one hand. It should not be heavier than you can carry it for a long period, but not too light.
The stick is held horizontally pointing in the direction you want to go. It works as an inertial navigation aid. If you turn, then you can feel it in your hand. If you encounter a bush, then push it straight through. Then you can walk around, pick the stick up and continue.