I have been ready for WWIII for a very long time. I am ready at a moments notice to leave to my bunker. They key to survival is the first two weeks because that is when the most casualties happen because of radioactive fallout.
You raise an interesting point, but who wants to stay underground for a full two weeks? I'd go crazy with cabin fever.
In my scenario, just as the bombs drop I invite a couple of nubile coeds from nearby Rice U into my shelter so as to make the time pass more quickly and to repopulate the earth afterwards. For some reason my wife keeps giving me flack about that aspect. I tell her it's my duty!