Therefore, in such a doomsday situation you have to come up with a situation in which you can trade with people in order to survive. There are two solutions I can come up with, either using precious metals such as Gold & Silver or using Cryptocurrency. Considering that fiat currency is useless, Cryptocurrency might raise in value so that it can be useful as a means of trade as long as the Internet still exists which will most likely be the case.
Economics recession is different from doomsday, fiat will still worth something as long as a country still has something as back up such as gold reserve.
The most important thing should be the agriculture industry to provide enough food for citizens.
Doomsday will happen after the nuclear war, which means the internet will go down i.e vanish, so does bitcoin.
in this case, even gold will lose a lot of its value, food and clean water are the 2 most important commodities, that's why if you watch National Geographic where some people prepare for the doomsday, they built fortresses, equipped with weapons in order to protect themselves and their food supplies from others.