I think your interest in saying "we've got to figure out the pop culture!" in these apocalyptic scenarios overlooks that so many people will be dead and thinking of simply trying to survive to worry about this stuff. No one is going to have the luxury or time to craft urban legends.Speaking of that, I'm sure the gold reserves at Fort Knox would have been forgotten. Many years later, perhaps even centuries, it would become a myth just like Yamashita's gold.
There's not going to be pop culture when there are only a few humans left. We'll be lucky if we avoid extinction.