What’s interesting is that if your fallout shelter is dug into the ground (at least ten feet under) and contains a decent way to seal out contanminants, you could survive a near-miss from a 1 MT nuclear bomb (though ground zero has to be around 1.75 miles away) and live there safely for up to 2-3 weeks with enough consumables such a water and canned food. Mind you, those shelters now find better use as tornado shelters in the US Midwest.
Tho, of course, what would one do 3 weeks later, is quite an interesting question.