Earlier quoted context omitted.
Unless you think the bombs are going to fall, you'd be better off getting some sort of cabin than a bunker. Living underground has a lot of challenges; it's expensive to build down there and you'll constantly be fighting moisture and mold.
I think the threat model is packs of desperate people looking to take your stuff, not bombs.
All in all, it seems like a hopeless scenario. A better approach is probably to make friends with your neighbors and try not to look like you have anything worth stealing.