Apples

Active constituents: pectin
Apples of all shapes, colors and sizes can be found in the wild.  Often they are trees that had been planted on a farm within the last century and sometimes you can find an abandoned orchard.  The apples won't be flawless; they may be worms, rust, spots, deformed apples, and bees will be attracted to the fermenting sugars.  Most of these problems are cosmetic and can be cut away, leaving a good portion of the flesh to eat raw or use in recipes.  Another wild apple cousin is the crabapple,a much smaller and non-cultivated version of an apple.  They tend to be more tart than planted apples, but still contain lots of pectin and can be eaten raw if you don't mind sour apples. 

Sources
Adventures in Edible Plant Foraging