Wind blowing through trees, crickets chirping, crabs, and walking sounds; Forest/Woodland leaves crushed, water splash, tree crashing sound & louder chopping.
It's not many but would make a huge difference to being out there. I know the would is mean't to be wild and empty (and scary).
Perhaps an uncommon Eagle which hunts rabbits, snakes, players and makes cry (good reason to carry a musket).
[please do NOT add this to Small Suggestions, I feel this is a major effect which will create real immersion, currently there is no point to have sound on - except snakes, (that town music is a horror for the ears). I do not want this to be lumped in with the massive Small Suggestions thread where it will be forgotten about until the last minute.]