There is nothing you can do. No one ever has managed to prepare himself for the war, you just can't be prepared for something so terrible. And it's worse than in your worst dreams, beleive me I've been there. And WW III if it happens would ruin man kind, the survivors would have to start again from nothing, from the very bottom.
You can not be exactly prepared for war, because it usually always starts unexpectedly and bears a lot of losses.
Even if you have a supply of food and basic needs is not a guarantee that you will survive. If a nuclear war would be the fact you need to have a bunker to build a bunker very difficult. Also you can just kill or Rob. This margin during the war this wealth.