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.
Survival skills
A lack of water causes dehydration, which may result in lethargy, headaches, dizziness, confusion, and eventually death. Even mild dehydration reduces endurance and impairs concentration, which is dangerous in a survival situation where clear thinking is essential. Dark yellow or brown urine is a diagnostic indicator of dehydration. To avoid dehydration, a high priority is typically assigned to locating a supply of drinking water and making provision to render that water as safe as possible.