Universal
What you do depends on why you left
The techniques are the same everywhere (see the biomes and the tech tree) — what changes is your priorities and how careful you are.
Nuclear threat: the first minutes decide everything. Time, distance, shielding: the thicker and denser the mass between you and the source, the better. When you get into shelter, take off your outer clothing and leave it outside — that removes up to 90% of the contamination. Stay in shelter for at least 24 hours: fallout peaks in the first 24–48 hours. Closed water sources are safer than open ones for the first few weeks.
Epidemic: the same survival core, plus boiling water without exception and isolating anyone who falls ill.
Being chased, hunted, conscripted, dispossessed (it all comes down to one thing — not being found): a fire with no smoke, or at hours when it shows least, leave no paths and no tracks, and camp out of sight of roads.
"Fantastical" scenarios (zombies, invasion, AI): the logic is "a hostile opponent who will not talk" — the same principles as above.