North America is a huge and diverse place. There is no singular pre-Columbian diet. Agriculture developed twice in North America, first in Mesoamerica by at least 8000 years ago then independently in the Ohio / middle Mississippi valleys beginning around 5000 years ago. Mesoamerica gave us things like maize, beans, and tomatoes. The Midwest gave us things like sunflowers, pecans, and certain types of squashes. There were also a lot of other species domesticated in the Midwest that eventually became less important or dropped out of practice entirely - things like goosefoot (a relative of quinoa), marshelder, maygrass and little barley. Around 1000 years ago, maize swept through eastern North America and displaced many of the older crops. Beans followed shortly thereafter. All together, maize, beans and squash make up the iconic Three Sisters farming complex that was common throughout most of eastern North American when Europeans arrived.

As for bison, people have been hunting them for as long as there have been people in North America. Prior to the introduction of horses, popular hunting techniques involved herding bison of cliffs or into temporary pens where they could be killed more easily. People didn't follow the herds like they did once they had horses. So they either waited for the bison to come to them, or in some cases would make annual trips out to where they knew the bison would be.

For some specifics, you'll probably be interested in this question, which has answers from myself and /u/RioAbajo concerning the (north) Eastern Woodlands and the Southwest respectively.

Native Americans were also stone age people. Was the original tomahawk made from stone? How did they manage to produce the modern tomahawks made out of steel? Was it just some random axe they found and then just named them tomahawks? CMIIW.

The original tomahawk was made of stone. It was specifically a Powhatan weapon, though other nations had their own variants. Here is a post about Powhatan weapons if you want to know more about what they were like before European colonization. The metal tomahawk you're probably familiar with began as English boarding axes used and traded by sailors. Eventually, these axes proved to be such a popular item that the colonists started making tomahawks specifically for trade - the pipe tomahawk being the final form of this concept.

That said, Native Americans as a "stone age" people is erroneous. The Old Copper Complex around Lake Superior was producing copper knives and spearheads 6,000 years ago. These metal weapons largely went out of fashion by around 3,000 years ago, but people were still producing copper items for a lot of different purposes. Mostly it went into creating artistic and ceremonial items. Some of those took the form of weapons, like these copper axes used by various Mississippian societies. Judging from the wear and tear, or relative lack thereof, it doesn't seem like people were using these as mundane axes.

I can speak for the natives in my area, North Dakota, which, if you aren't familiar, is basically the center of the continent. The natives I'm most familiar with are the Mandans (rhymes with can-cans) who lived along the northern Missouri River.

The Mandans, first off, were agrarian. They lived in reasonably large towns of buildings called earth lodges, which look something like hobbit holes, surrounded by wooden palisades and farms. These farms would grow things like squash, corn, beans, sunflower, and tobacco, which is pretty impressive, given our rough climate. Excluding the tobacco, these would often be eaten boiled into a sort of stew.

In the winter, they would hunt. The town would pack up and move to the frozen river and establish a settlement. This settlement would be a large ring of tipis. At the down-river end of the ring, several Mandans would chip a large hole in the ice, while others would try to find a bison in the area. They would chase the bison onto the thinnest part of the ice, where he would fall into the frozen water, drown, and float downstream. The down-river Mandans would then haul him out.

This bison, called float bison, was considered a delicacy and was enjoyed aged. Explorers like Lewis & Clark, Prinz Maximillian zu Wied, and George Catlin were disgusted by this practice. One explorer refers to the meat as having a green sheen, and weren't keen on trying it.

I hope this helps!

Native Americans are as varied as Europeans. Go from region to region and you'll find different tribes with different ways of life. In the Great plains they hunted Buffalo even before using horses by either lying in wait to ambush passing herds (migration routes rarely change) or using sites like [http://www.history.alberta.ca/headsmashedin](head smashed in Buffalo jump) to chase Buffalo off a cliff and to their deaths. More Eastern tribes like the Iroquois Confederacy relied on farming, and several coastal people's relied on regular fish spawning runs to harvest and supply their tribes for the season

For the Northwest Coast:

King Salmon, deer, chum salmon, whales, Chinook salmon, clams, sockeye salmon, mountain goat, Coho salmon, seals, pink salmon, halibut, black bear, various roots, huckleberries, crabs, oysters, octopus, cougar, beaver, sea lion, loons, mallard ducks, seaweed, kelp, strawberries, cattail stalks, elk.

Mainly seafood with wild game and plant foods supplementing.

Source: Feeding the People, Feeding the Spirit: Revitalizing Northwest Coastal Indian Food Culture.

And steppe people also tend to remain nomadic. Never went pass the domestication stage. The Mongols are another example of steppe culture who remained nomadic and never developed farming. CMIIW.

Most if not all of old world nomadic cultures (Asia, Africa and Europe) use domesticated herds. Its the new world that are the exception, (possibly due to lack of domesticated cattle?)

Pastoralism does not necessarily clashes with farming, but nomadism does, so obviously there is no need to develop agriculture. That does not mean lack of awareness of it, as nomadic and agricultural settlements often coexisted and formed parts of the same political organisms.