lnhammer pointed me toward the storyTropes TVTropes entry on the Cozy Catastrophe, an alternative to the "only the mean/tough/etc. survive" end of the world scenario. :-)

I've been thinking for a while about how, just as we can rig the worlds of our stories to make them sympathetic to the ways we think the world does or should work, we can also rig the (fictional) end of the world.

So in the Ember books and, even more, in Life As We Knew It, the food supply and other essential materials are in a sense "rigged" as things we can't get more of--which becomes a way of keeping a power structure in place, because you need a system for distributing--or withholding--those goods. (That power structure breaks down when goods grow sparse though, or when it turns out there's a way out--which there is in Ember, isn't in LAWKI.)

Anyway, what you need to survive in a world like that are connections--to at least some of the people with access to some of the food supply. (This is strongly true in Life As We Knew It. In Ember, while we do find a way out--we then need to find ways to connect and work with the people with access to the food supply in the out we find.)

To survive in a world more like that in Hole in the Sky, where a virus wiped out most of the population, what you need to survive is something closer to self-sufficiency, or else the skills to be the sort of trader who helps other people be self-sufficient. A virus means you tend to live in small groups, not large centralized ones, which encourages self-sufficiency more, because any stray person--any stranger--could bring the virus and destroy you all. Or else you could be one of the lucky ones who manages, at cost, to be immune to the virus--and it's those folks who actually do throw a wrench in the works of the society, because they're playing by different rules.

If you want a world in which the spoils go to those with the most guns and ammunition, you have to make sure the world ends in a way that lets the guns and ammunition survive, or else you have to leave enough infrastructure behind to make more. If you want cooperation to be key, you have to make survival hinge on something that requires cooperation--successful agriculture, say; or maybe needing to keep a big bad from breaching your cooperatively-built town walls. Everything from what how the environment changes to what governmental and physical and infrastructures remain in place rigs the sort of world your playing with. If you want engineering and cleverness to be key, throw the world into a deep dark place that only engineering and cleverness can get it out of.

Or you can have a cosy catastrophe, where things are rigged so that life more or less goes on, and folks don't sweat the end of everything so much.