Yesterday in the comments, Grilltech asked about what N America had contributed to the produce department, and I'm sad to say, my first thought was "precious little". Off the top of my head, I could think of only two plants native to N America that went on to become major (or at least widely available worldwide) food crops; sunflowers, and wild rice. That's not to say native Americans ate nothing else. But those were the only two crops I could think of immediately that everyone worldwide would likely have heard of. There are more, now that I've done some research, many of them available worldwide, but none of them are what we would call a staple crop like wheat, or soy, or beans, or rice. The ones we've got were often tricky to domesticate, and N America never had a grain-and-legume combo that mankind needed to found advanced civilizations. (Polynesians being the exception to that rule.) See, it's complicated. I'll be thrilled to explain.
No one is quite sure how the processes of plant domestication, animal domestication, settlement, and civilization building happen, and nearly everyone agrees that it varies. Some people domesticate crops first and then decide to settle down, some settle down and find foods to grow, some, we just don't know. In north America, domestication seems to have been low priority because in many places (not all, but many) such as the Great Plains, Eastern Woodlands, and Pacific Northwest, they had such plentiful food that there was no good reason to domesticate anything. If you can walk out your door and pick food off a bush, why in hell domesticate? It's more trouble than it's worth unless people are starving. So, near as we can tell, no great cities were built in N America until the Three Sisters were 'imported' from C America, up along the trade routes. Eventually N America got heavily populated enough to need to grow some food, so people planted the Three Sisters and lived off those. A few other things got domesticated (like sunflowers) at that time, but the Three Sisters were so efficient in terms of calories per acre, that there was no motivation to find anything local to domesticate. And really, there were no grains or legumes in N America that could compete with the Three Sisters, even if they'd tried. Eventually some large cities got founded (some Moundbuilders, Pueblo culture).
I'll give a general list of food crops that are native to N America; many of these were gathered, not domesticated, until after Europeans got here. But they are native, and were eaten by native Americans in the areas they were native to. I'll make comments where I've got something interesting to add.
-elderberries; very small and time-consuming to gather, make good wine.
-American grapes; related, but not identical to, European grape varieties. These DID save the global wine industry. They are the only species resistant to several pests, and to this day, all grape varieties world-wide that are grown for wine are grafted onto American grape vine roots. Every. Damn. Vine. (This could be another blog post if anyone's interested.)
-red and black raspberries
-assorted varieties of plums, cherries, and crab apples (all rosaceae species)
-cranberries, which are insanely sour without big piles of sugar added; of course native Americans didn't HAVE big piles of sugar
-paypop/lilikoi/passionfruit (there's that folk name thing again)
-prickly pears, the cactus fruit
-lupin seeds, not from a grass and therefore, very technically speaking, not a grain, very time-consuming to gather
-nipa grass, native to arid regions of the southwest, produced a very small but true grain; it is resistant to salty soil, and is being investigated as a 'new' food to be introduced to troubled areas around the world
-wild rice; there are three species native to N America, all were eaten by native Americans, and they have only been grown commercially since the mid 20th century
-cattail; they ate the roots and the pollen - I've read about that for twenty years and still can't quite get my brain around eating pollen
-goosefoot/pigweed; the seeds are about the size of a mustard seed and pretty tedious to harvest (quinoa, the popular 'new' grain food, is a closely related species, but native to S America)
-acorns/oak trees; really bitter, but edible
While not a food, tobacco is probably native to N America (no one's quite sure; it's native to the New World for sure, there's just debate as to exactly where). It's become a major cash crop world-wide.
American Chestnut trees produce nuts that were eaten by native Americans, but when European settlers came to eastern North America, they brought pigs that were turned loose in the woods to forage on the nuts. In most of Appalachia, the people lived on those pigs and what they could grow in kitchen gardens. When the chestnut blight hit in 1900ish and killed the chestnut trees, thousands of people had to leave the Appalachian mountains and move down into the cities and find work. Many became textile workers in the mills of the south.
So there you go. N America did produce foods that have since been grown commercially, but none of them are a major, immediate go-to food. At least not for most of us. For anyone who is finding this discussion interesting, particularly the relationship between available foods and 'civilization', I suggest reading "Guns, Germs, and Steel" by Jared Diamond.