From the dawn of Man we have learned (and, perhaps, learned from other animals, too) that there are 5 basic human needs for survival:
Without these five things, eventually we perish. For more information visit survivalsavior.com
Try this experiment. Take a deep breath and hold it in. Time it, if you can, but hold it as long as you can. Now exhale as slowly as you can. It is disorienting, isn’t it; and it didn’t take that long, did it? Now do this: take a breath and exhale, pushing all of the air out of your lungs and hold it. Do not breathe in again. It is amazing how more quickly aware you become of your lack of oxygen.
In most cases, you are not going to be deprived of oxygen to such an extreme but if, for example, you are trapped in a fire, the more contaminated air you breathe, the less oxygen your body will get (and the more toxic your lungs will become), resulting in cardiac arrest, organ failure, stroke, etc.
Just 15 minutes without oxygen can result in irreparable brain damage.
The human body is made of 60 percent water. Water lubricates the blood vessels, the brain, the joints, and even the air passages. We need it to digest food and to keep our balance.
Depending on various conditions, the human body can survive no more than 10 days without water (though it is probable no more than 5 days).
Once you secure water, you can set about finding food. The good news is that the human body will subsist on fat reserves (the first few days) if no new food is introduced/consumed on a daily basis and this can go on for several weeks. However, muscles and organs will begin to break down.
The human body can survive between weeks without food (though typically death is the result not of starvation, alone, but of the various other health issues that arise from it).
SHELTER and SLEEP
You will not, necessarily die from lack of sleep. However, lack of sleep can result in other problems with cognition and memory. Equally, a permanent shelter is not an absolute necessity. However, establishing a permanent shelter does ensure that you can store food and even water and that you are able to get enough sleep.