I think this might be one of the reasons zombie a apocalypses are so popular because it gives a plausible reason for why large groups could be just as failure prone as small groups, as well as a plausible reason as to why the survivors don't just immediately restart society considering the infrastructure, power stations, and factories don't just disappear but require the knowledge and logistics to run or maintain them and some essential people might have been turned into zombies, plus the risk of attacks while doing maintenance or going out to run it.

There’s a Cory Doctorow short story, “The Masque of the Red Death”, that’s exactly this: a bunch of rich, ultra paranoid preppers get together in a bunker after societal collapse. They’re all incredibly selfish and eventually turn on each other. Meanwhile, everyone else cooperates and gets along just fine to survive.

I have been in a flood that turned the land into a lake, horizon to horizon. Densely populated. Utterly devastating. The railway was elevated enough to get between two mid-sized cities, and on the 12km trek I saw an amazing amount of compassion, mutual aid, and casual, natural-feeling grassroots organization to just get on with life.

I have been in a few crises and minor disasters, come to think of it. I think generally, most people like banding together and helping out when shit gets crazy.

"A paradise built in hell" by rebecca solnit is a great book about spontaneous co-operation during disasters