If you're warned of an imminent nuclear attack, be sure to move towards the expected epicenter of the blast. You'll want to be vaporized rather than cooked alive or suffer fatal radiation sickness (over the period of days or weeks). You'll want to be spared the horror of watching others die and society quickly unravel. You'll want to avoid being a burden on the non-existent safety net that won't survive.

Watch "The Day After". It's probably the most realistic depiction of a post-apocalyptic situation to date. (It's not dramatic and cool, or cinematic--long, boring, and flat out horrifying.)