The only kind of foraging i have ever done really is at the beach, i used to enjoy collecting cockles, then taking them home to eat. Cockles are small salt water clams which you collect by raking them from the sand at low tide. They were in abundant supply in Devon where i used to live.
I wonder how safe they really are to eat collected straight from the beach, i always used to boil them and then season them with vinegar and pepper, so i assume they were OK as i boiled them, i never suffered any ill effects but i would worry these days about the amount of pollution that is pumped in to the sea, you can't be too careful with seafood.