People apparently forget that if something very bad happens, whether it is a global war or a major natural disaster, we can expect that there will be serious disruptions in communication or, better said, an interruption of the internet. If that happens, the things that will be most valuable will be food, drinking water, and medicine, and of course, means of self-defense.
Of course, we should not be pessimistic, just realistic and prepare in time for every possible scenario.
People forget history like it was nothing but they repeat it constantly and they make the same mistakes over and over again. War it's a situation that doesn't leave anything untouched and nothing can work properly. I agree with what you said about basic things that will be missing and digital currency is not among them. However, I disagree that you can be prepared for such thing unless you are living already in a war zone country. Even in this case, getting things for your survival isn't preparation.