Don't bother preparing, if anything happens you'll be dead anyway.
exactly. death is certain, either immediately or inevitably...i choose immediately being flash fried by a nuke, surviving the blasts would only lead to a slow agonizing death from starvation, suffocation, radiation sicknesses, etc. there's so many slow horrible ways to die that its better to just sit on your roof and watch the pretty fireworks. Also i'm pretty sure that we won't have any warning of such an event...countries won't announce "hey we're about to end the world by pushing buttons so we'll wait an hour for you to grab your friends and family and get to your bunkers".

That's what the books are for. Just remember to bring matches.
Unless you have a generator and plenty of fuel.
matches and fuel burning generators will use up your most important resource, oxygen. I think people don't factor oxygen into such situations because we all take fresh air for granted. You would not only need to pressurize your bunker to make it airtight but you would need some sort of ventilation to remove all the carbon dioxide and other gases that you and your family would be expelling as that would quickly contaminate your air.
Are we talking Falloutish nuclear war, or The Road nuclear war, because of it's the more realistic latter, I think I'm just going to off myself.
this is the problem, people play way too much fallout and watch too many movies...realistically it would be almost impossible to survive a worldwide nuclear war. At best you can survive the initial "war" but you would only temporarily delay the inevitable