Being in California and preparing for wildfires and earthquakes for the few days before the civil authorities reassert themselves and things return to "normal"? A good idea. Anticipating an incident which collapses civil authorities beyond the point at which they can recover? Not only does this feel psychologically unhealthy I think it also ties into pro-collapse politics that actively speed up this outcome. Also tied into the deep American fear of that which pervades everything.
The fire is just a bunch of (waterproof) matches and a few cheap Bic lighters and a german military stove from an army surplus store. Cost me maybe 8€ a decade ago.
Going to weeks or months start to be reach.
And beyond that, what are you expecting to come back to? Subsistence farming? That is a very large step up... And well then you have lot of people to compete with. If we are talking about total systemic collapse, well that is very complex mess to prepare for.
On other side large scale wars, well probably some support will come relatively quickly.
And the old trope about ammo becoming currency, has this ever actually been a thing anywhere?
IIRC, Mormons store a few months stockpile as standard.
* For an unhealthy diet, my university meal planning for a significant fraction of each semester was two large bowls of cereal in the morning and ramen noodles for dinner. I didn't realise how far below my caloric requirements that was until comments on this forum many years later. But that cost 50p/day in the UK in 2004, and if you're consuming 500ml of UHT milk/person/day then the six litre multipack one person can lug up a hill with no car will last 12 days before needing replacement, while dried grains and cereals like oats, rice, etc. are even easier to stockpile.
Food storage is not just for apocalypse type stuff. It's for what the heck ever.