I can rec wild strawberries and wild garlic (ramsons); both cope with shade fine, and the wild garlic seems to thrive on complete neglect too.

It might also be worth asking in permaculture, since building an "edible landscape" that integrates trees is a key permacultural approach.

As a random piece of data: you're going to have to watch how closely you plant things to the black walnut -- it secretes a chemical into the soil that can stop various other plants from growing.