The rules of the fours:
Under extreme circumstances, human survival is roughly based on-
4 hours of exposure, seek or keep shelter. Hypothermia and hyperthermia kill quickly.
4 days of water. Without exertion the average person will dehydrate in 96 hours.
4 weeks of nutrition. With minimal exertion the average person in good health can subsist on minimal nutrients.
4th variable is that any of the combinations of the above are exacerbated by illness or injury. Always have a plan and itinerary with two trusted sources.
Existing medical conditions or handicaps must be accounted for. Hopefully this man is adept at survival.