Even if you survive the initial blast, and the radiation sickness doesn't get you - the black smoke would hit the jet stream, above the rainclouds so no way to wash it out, and cause a nuclear winter. Apparently, 99% of food would be impossible to grow and most would die of starvation. And stockpiling won't save you, because looting would become endemic. Very starving people will eat your food at best, and you at worst. So your death would be 1) medically horrific (radiation sickness, or burns) 2) violently horrific (murdered, and possibly eaten) or 3) slowly horrific (starvation - and watching your kids starve).
Even people like the Zuckerbergs, who allegedly have a bunker in New Zealand with a large farm above it, would be at the mercy of their armed guards. They'd better hope the guards like their employers. A lot. Because after a nuclear war, that goodwill would be all that protected them from being evicted up into the open, themselves. And are they planning on bringing a range of doctors with them, too? A fully equipped operating theatre, radiography centre, range of drugs? What about people who can fix the air, water, sewage and energy supplies necessary for that bunker to stay safe, clean, lit and fed? Are there hydroponics, or just dried and frozen and tinned food? Does anyone have the knowledge to start farming after 20 years or so, when you emerged back upstairs? Where do your kids's friends and eventual partners come from? You'd need to create a small town underground in that bunker for it to be remotely worth doing, just for a very simple form of life to be worth living, let alone have any sort of quality. Are they doing that? Can even billionaires afford that - and how do they ensure all these people, and even their own families, are close enough to the bunker to use it, if need be? I mean, I doubt we'll get a calendar warning: "3 days from now, Armageddon." A 30 minute warning won't be enough to jump in a plane from Cali to En Zed, will it - not for any of the team. Most likely scenario, as far as I can see, is that whoever is stationed in any such bunker would get to use it, and the people who funded and built it might well not, as they can't reach it in time. Unless they want to move over there and stay leashed to within a 30 min drive (or helicopter ride) of that bunker main door.
That's the billionaire dilemma. For the rest of us, it's pretty simple.
To come off best from a nuclear war, live in a place likely to get bombed directly, early on.