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.
Infra-Worlders
The Infra-Worlders are a society of humans led by Captain that has lived for five decades in a gigantic submarine named the "Infra-World." These humans have been "evolved" so that their bodies can withstand the water pressure at 5,000 fathoms beneath the ocean's surface; as a result, they cannot live on the surface of the world.