When I'm thinking about this stuff I'm usually just thinking about having something already built off the grid so that if shit ever does hit the fan I have a backup plan that isn't squatting in the woods. I'm not leaving the city until it's burning. Well, burning more than they are right now.
I think it's much easier to just have a nice little country home that could be transformed into a real shelter on fairly short notice and doesn't cost that much to keep open (which it shouldn't if it doesn't have utilities). Then you just hope you never have to put it to the test, because the transition is anything but guaranteed.
Shit, if nothing else it's good to be like those rich NY fucks who run off to their vacation homes whenever there's unrest among the proles.