Would it be hard to live in the wild ? Eating plants and animals and sleeping in a cave or hut?

Not if you adapt to that lifestyle.

People do but it is a lot easier to just go to the store for your food. All the plants and animals you buy there were once wild (or their ancestors were). If you are interested, get a copy of one of the US military survival manuals and read up on edible plants, trapping, etc. I like the one put out by the army. There are also good books by Muencher and by E. Lawrence Palmer.

As far as sleeping in a cave goes, it depends. Some are wet, some dry. Once you get beyond the entrance, the temperature remains the same throughout the year. That might be comfortable or not.