Living in suburbia, downwind of New York City, my rational choices do not include sitting it out. I will likely survive somewhere between hours and days in the event of thermonuclear war. In the event of complete infrastructure collapse, regardless of the cause, I give it a month. Going full prepper here is a fool's errand. The only reliable source of fresh water is 1200 feet down.
It obviously isn't optimal, but this is where I have to make my stand.