Basic Survival

Your character will have 3 things to worry about.

Hunger is depleted over time and if you have a mutation which excretes something.
Thirst also depletes over time, but is heavily influenced by your mutations.
Stamina is one bar that stretches across the bottom of your screen, and drains throughout the day from your actions. It is replenished by sleeping at night, and can be strained to cause further draining from a lot of actions at once, a long period of action without stopping, or various ailments.