This is what made my maternal great aunt such an incredible person. She survived the bombing of Dresden, the loss of many family members in WWII, the collapse of Germany at the end of the war, and many years in communist East Germany. When my sister and I would ask what drove her, it was always "survival." The simple act of refusing to lay down and die.

It is much the same advice that I give to depressed and overly stressed kids who are approaching their breaking points. Divide everyone you know into "us and them." The cancerous, poisonous types who mean you harm and the few who genuinely want to help you. A great many kids already face a "bunker mentality" with parents or relatives that no longer with to deal with them.

I went to lectures and presentations by special forces members in college. Their level of training and preparedness is remarkable.
I am not sure what branch of the armed forces does this, but I recall hearing of an exercise where trainees are left in thick woods or swamps for a week at a time, with very few supplies, and told to survive or else.

A question once posed in a seminar on mentality -- how would you react to being in harsh, life-threatening circumstances where others have shelters and supplies and you have nothing? Best answer I heard -- figure out a way to take over the shelter.