You can’t survive in survival bunkers or islands, and thinking otherwise is a pipe dream. We don’t have a true model of what this might look like, but if there’s extreme instability then wealth doesn’t serve as a safety measure—it will be a target. You need backing by governed armies to protect status and wealth, but in some proto-civilization model, there will just be warring factions with bunker busters and maybe nukes going at each other. They’ll eventually form treaties and merge into city states, repeating the same trend towards nation states and democracy. Just skip the dumb bloodshed in the middle, and settle on Nordic socialism from the get go.