This group stresses being able to stay alive for indefinite periods in life-threatening wilderness scenarios, including plane crashes, shipwrecks, and being lost in the woods. Concerns are: thirst, hunger, climate, terrain, health, stress, and fear. The rule of 3 is often emphasized as common practice for wilderness survival. The rule states that a human can survive: 3 minutes without air, 3 hours without shelter, 3 days without water, 3 weeks without food. 
Survivalism is a movement of individuals or groups (called survivalists or preppers) who actively prepare for emergencies, including possible disruptions in social or political order, on scales from local to international. Survivalism also encompasses preparation for personal emergencies, such as job loss or being stranded in the wild or under adverse weather conditions. The emphasis is on self-reliance, stockpiling supplies, and gaining survival knowledge and skills. Survivalists often acquire emergency medical and self-defense training, stockpile food and water, prepare to become self-sufficient, and build structures such as survival retreats or underground shelters that may help them survive a catastrophe.
Earthquakes, tornadoes, and hurricanes can cause you to leave your home or even be trapped there. Roads could be blocked due to fallen trees, power lines, or even damaged earth from the natural disaster. Rescue crews can not be in all places at once. You may have to wait it out for quite a while before its over. You won't be able to go to the store or to the corner market.