There are overcasts and there are overcasts. Today was complete cloud cover in my neck of the woods, but you could still see the bright spot in the clouds where the sun was now standing. Sometimes you can't and then you are in a pickle.

Even better is night time. Learn to recognize the Big Dipper, its pointer stars and the North Star. You will have True North nailed. I used this once on an early morning start on Orizaba, the highest of the Mexican volcanoes. My companion was using his compass when I pointed out the North Star. His compass was off by about 34 degrees due to local variation (local rock with high iron content).

Prehistoric Polynesians explored and populated the entire Pacific,navigating by wave swell patterns, flights of birds,changes in the sky tint over islands,and all kinds of esoteric lore.