I manage fine in the woods without a knife, but it's sort of leaving home without wallet, keys and cell phone. Even if i don't need them all the time i feel naked without them. There is no real need for a knife when building a shelter, starting a fire, digging holes etc. The only time it's hard to manage without a knife is when detailed precision is needed or when what you can find in the woods isn't strong enough to pry, dig, poke etc.

That said, i love my knives and i carry at least one almost all the time. I jump at every opportunity to use them because most cutting-ish tasks are easier and more fun to do with a good knife than with something else.