After reading through this thread, I realise my base assumptions are rather different. Maybe I'm naive (or Australia is v different to the US? not sure) I don't see anyone thinking about relying on friends, family, the local community or government in case of disaster. Or maybe it's that bushfires are the only event that's likely to impact directly on my city (flash flooding and big storms have more minor impacts). The last big fires destroyed 500 homes, took out one sewerage treatment plant and contaminated a couple of our drinking supply dams for a year or two, power was out in some suburbs for a long time, but... nobody affected had to fend for themselves.
Our government has a well-oiled machine of emergency funding handouts of around $1k if you've been badly affected by a natural disaster (bit painful to get if you lose all your ID, but not impossible) so you can get some clothes, food etc, charities get involved etc etc. Longer term recovery from major disasters is not always smooth or equitable, but in the immediate aftermath, there seems to be a lot of support from community, government, friends, family and the like.
I try to avoid overly paranoid thinking cos it's not helpful/healthy for me personally (I tend to withdraw from my social networks and feel like I'm deprived, can't share anything, must keep everything to myself, don't help others etc etc). That's probably entirely due to my own personal hangups and childhood environment, so YMMV.
Edit: I'm also probably a bit fatalistic about thinking about disasters/wars/zombie apocalypses that destroy infrastructure/society. Insulin keeps me alive, and needs to be refrigerated. If things are that bad that refrigeration/big pharma is unavailable worldwide, I'm dead within several months regardless of how well my home is prepped. So I plan for 1-2 weeks of self-sufficiency at most. Maybe a month.