There's one thing prepper fantasies have in common... the impending doom never comes. It's fun to think about. But, real honestly, if the survivors at Hiroshima and Nagasaki were able to get by in the days after their tragedy, I bet I could figure something out on an ad-hoc basis.
If you look at history, a lot of wars were won or lost based on how well a city prepared for a sustained siege.
in the case of hiroshima, water pumps were restored 4 days after the bombing, but of course the story is more involved (http://www.hiroshimapeacemedia.jp/?p=47988)
> devolved into small groups of people who didn't share food.
In what context did this happen? Doesn't sound like a fun camping trip
There's a saying: "civilization is only three meals away from anarchy", that only made sense to me after day 28.
tl;dr - All you need is a bathtub, a WaterBob, and 10 teaspoons of bleach.
The average bathtub holds about 80 Gallons of water, that's enough for two and a half people for 30 days. The rule of thumb is one gallon per person per day. See: https://www.beprepared.com/blog/18680/much-water-store/
I always have a few of these things called "The Water Bob" stored in a closet, a few cause QC isn't that great. Its like a giant plastic bag that sits in your tub and holds water.
You can add 1/8 teaspoon (or 8 drops) of household bleach per gallon to get potable water. See: https://www.cdc.gov/healthywater/pdf/emergency/09_202278-b_m...
I only know this cause I lived over seas during the first gulf war, and we had to have prep stuff for scud attacks. We didn't have the WaterBob, but there were plenty of 50gal plastic storage containers. When the sirens went off, we set the jugs to fill in the showers, and hid in our inner most room. Fun times all around really. Free gas masks though! So that was nice.
The items I describe fit on a single shelf (except the water; I have a water filter and a nearby stream, so I only keep a few liters on hand).
I'm just a backpacker though not a doomsday prepper, the stuff we carry isn't always appropriate for an emergency situation and is generally geared towards being very portable rather than robust/100% reliable.
I've lived for 30 days in alaska on a glacier with only what I could carry in a large pack; water and fuel were the largest by weight, sleeping bag/tent/clothes were the largest by volume. By the end, campers had devolved into small groups of people who didn't share food.