If you have
Gaia's Garden, you might want to review his sample guilds. He specifically mentions the possibility of replacing an Oak in a guild with a Chestnut because the trees are in the same family of plants. Looking at what he chose there it was smaller fruiting trees, shrubs and hazelnuts.
Also following that reasoning, you might be able to find existing gardens or plant communities under
local oaks to look to for suggestions. Are there any wild foods that are common in your local woods? Even if it's barely palatable, there's probably a domesticated relative that would make a good alternative.
A little hunting on Google produced this page
http://nativeplants.msu.edu/plant_facts/local_info
Click on a region and you get a charts of plants and growing information. I recognize several food and nitrogen fixers.
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