Really intelligent thinkers over the centuries have had some strange ideas about how humans survived in the pre-civilizational ages. Thomas Hobbes for example, political theorist/philosopher/author of The Leviathan, saw this early man as always walking the blade's edge between survival or death with "nature red in tooth and claw" just behind. Hobbes was writing in the 17th century, before Darwin and the idea that humans were simply more specialized adaptations on nature's earlier models, but his idea has held even up to present times. The idea is so popular, even though it contradicts our knowledge of humans as social creatures (maybe philosophers aren't very social), because it serves a purpose. The message is that without civilization and the society you are born in to, then you face a bleak existence with death ever-present, so be thankful for what you have.
Early humans however were not ill-prepared for the environments they lived in. Sure, we don't have the body hair or girth of a gorilla. Alone, we make easy prey for tigers. We lack the sharp claws and teeth of a wolverine. Our skin is soft, and our bowels are exposed. Nature does not leave her creations without what they need to survive. We come equipped with a vastly superior problem-solving brain and the ability to communicate solutions to our descendants, allowing them to in effect stand on our shoulders.
Early humans adapted to live in the same way that our genetic ancestors did, by living in extended social groups where people specialized in specific skills. This is called the tribal system and basically consists of many clans with a clan being roughly equivalent to the modern extended family, all your cousins and second cousins, nieces and nephews. Members of a clan would often specialize in something like healing with ritual and herbs, but everyone member would have basic knowledge about what to do in case of a snakebite or broken bone. Clans would also specialize in their relationships with neighboring tribes, based on where the clan resided in their tribal territory. They would have a few members who knew the surrounding tribes' language and culture to aid in maintaining friendly trade relations and to diffuse hostile situations.
As for the weather, humans adapted to almost every climatic extreme several thousand years before experiments at civilization-building. The igloo, the tipi, wigwam, the use of animal pelts and cob (mixture of straw clay and sand), and wooden homes built high on stilts (preferred by Sawi of New Guinea). The tipi for example was constructed to hold heat in the winter from a central firepit while pushing smoke through an invisible chimney out a small hole in the top. During the summer on the Great Plains, this structure would fold open a bit and allow the easy escape of excess heat. On top of that, these were movable structures designed by a nomadic people. The point is that every tribe had a lifestyle based on tens of thousands of years of accumulated knowledge about what works. Comparatively our civilization is a baby that can't grow up, because we keep destroying our accumulated knowledge or discounting it as old-fashioned.
The tribal lifestyle still exists for those who wish to see it. The Yanomami of the Amazon, the Bushmen of the Kalahari (at least those who haven't been removed by a government wanting to mine for diamonds), and the Gebusi of Papua New Guinea are still living in essentially the same way as everyone lived before the great exercise in civilization. These tribes are fewer and fewer every year due to further resource consumption by the civilized nations, so our chances to see what a time-tested lifestyle would look like is rapidly fading.