Shelter

You can survive for 3 Hours without shelter in a harsh environment (unless in icy water)

You can survive for 3 Days without water (if sheltered from a harsh environment)

You can survive for 3 Weeks without food (if you have water and shelter)

Fire

Fire is the source of life. Humans and animals cannot live without it because it provides light, heat, and energy. If you are in a situation where it is essential for you to have a fireplace in order to survive, then these skills are going to be worth a lot.

Water

At least 60% of the adult body is made of water and every living cell in the body needs it to keep functioning. Water acts as a lubricant for our joints, regulates our body temperature through sweating and respiration, and helps to flush waste.

The maximum time an individual can go without water seems to be a week — an estimate that would certainly be shorter in difficult conditions, like broiling heat.