My daughter is kind of becoming a horticulturalist and recently taught me that sumac (there are non-poison varieties) can make something akin to lemonade if you dip the berries into water and then filter the water back. They have a citric-acid-like outer shell that dissolves in water.

And we've eaten so many mushrooms and stuff - thanks to communities on the internet who have categorized lookalikes, where to steer clear of certain types (white mushrooms, don't even bother. Half of them will kill you)