
It was a mention of a secret, apocalypse-only regulatory code in Zuckerman's book that got me on the trail of the Code of Emergency Federal Regulations (CEFR), which I worked with the National Archives to make available to the public back in 2016: https://jasonlefkowitz.net/2016/10/presenting-a-bit-of-histo...
With a full scale nuclear exchange we would have a nuclear winter for a the first few years (when the radiation would be the highest). This is an interesting read that looks at actual US government procedures following and exchange. It's a bit dated, but was written during the height of the cold war. https://www.amazon.com/Day-After-World-War-III/dp/0670258806