On going straight
You forgot your compass. You're out in flat, featureless country, the sky has turned into heavy overcast and you want to go straight in thick bush. Get a "Swede compass," which is just a thin, straight pole. If you can cut a light one 20 feet long it will do, but longer is better, if it is small and light. Walk through the thick bush trailling the pole and you will go surprisingly straight!
If there is no sun, or prevailing wind, the moss on the basically north side of the trees will give a good indication of general direction.