On a food storage slant that got me interested in the whole survival and bushcraft thing, it is ossible to have a reasonable store, 3-12 months without being bonkers. figuring out the basics you eat in a week, and slowly doubling up until you have a rolling x weeks amount, then supliment it with the niceties etc. Buying smart will get you food that can last over the year and storage spacemay be a wall in your garage.
Water on the other hand is one dificult thing if you have no filter system or nearby source. Just a weeks worth of water for a family of 5 (like mine) is a LOT!
Im slanting more towards the individual 1 years worth of filter bottles and also a filter system for the brooks near my house.
I also know where the local rivers and lakes are.
Defense wise, I think it was Lofty who spoke about this in his book. Shops cleared first, allotments, gardens then known houses will be targeted when food is short.
You need to be prepared to do one of 3 things- 1) Hide and hope no one bothers you, 2) Share/loose what you ave to those more powerful/friends you have,
3) Be prepared to defend you and yours and what you have.
As others have said, the more of you there are the easier it is to defend, but you need more to survive.
In the UK, even if it got really bad guns will be in the minority, the tool of attack and defence in most parts of the world when society crumbles is the machette.
I know not too popular with bushcrafters here from what I gather, but a much more potent tool in that situation than an axe.