Hiking equipment
According to Tom Brown, the basic plan for survival is in the order of shelter (including clothing), water, fire, and food. Cody Lundin writes about the "Rule of 3s"; this relates to human survival without basics: three minutes without air, three hours without shelter, three days without water, or three weeks without food.
Eternals (comics)
Due to the cosmic energy that suffuses an Eternal's body and the nigh-unbreakable mental hold they have over their physiological processes, the Eternals of Earth are effectively immortal. They live for millennia, do not fatigue from physical exertion, are immune to disease and poison, and are unaffected by environmental extremes of cold and heat. Most cannot be injured by conventional weaponry, and even if they somehow are, an Eternal can rapidly regenerate any damage as long as they are able to retain their mental hold over their bodies; this mental bond can be broken however. In the 2006 series it was also stated that Eternals are able to absorb oxygen directly from water, and therefore cannot drown. In the same series, Ikaris was plunged into molten metal and experienced great pain, but no physical injury, which the Deviants attributed to a forcefield which protects Ikaris even when unconscious. It is unclear if all Eternals share this degree of protection.