Depending on the region of the country, the native peoples may have beaten you to it by a thousand years or more.
Along the eastern seaboard, to this very day, unattended for over 500 years, one can still find a species of Chenopodium called lambsquarters growing wild. You have likely pulled it as a weed from your garden. In pre-Columbian America, it was the number one edible green in the eastern half of the country, and it was cultivated in the semi-wild, as you are intending. It is also not an ecological threat throughout its native range.
European settlers brought with them various mustards, which have all escaped to the wild, along with other Brassica species. These are triploid plants which hybridize according to a genetic phenomena described by the Triangle of W. They will naturalize, though not as readily as lambsquarters. They are also no ecological threat.
Beyond that, focus on native fruits (paw-paw, sand plum, blackcap, elderberry, etc. for this region) and nuts (chestnut, walnut, etc.), though beware not to introduce seeds with blight, esp if there is no endemic chestnut blight in your area.