The third leg of the Tripod and the part that completes the bare minimum is quite simply heat. Water and food will keep you going but one really cold night and it is all over. We need to make sure that this area is covered as well.
I believe that when we are keeping warm our key tool here are clothes. Lots of them and several layers. A waterproof coupled with a good pair of boots and we can be warm even in the coldest weather. Even if we were out and about we could stay warm with the right clothes.
I don’t want to dress people so look around. Basic socks, vests, shirts, jumpers, trousers, jeans, jacket tops, over boots, hats with ear covers. Look at how the homeless people are dressed. They have those clothes for a reason and while you are picking their brains slip them a few quid. They are better set up to be survivors than most of us.
Bear in mind that most of us will be living indoors, there will be plenty houses abandoned and you should be able to find beds, bedsheets, quilts etc. There as well. Seal the gaps in the windows and you have yourself a nice nest. That is even without any generated heat.
Make sure you have as many changes of clothes as you think are reasonable. Same with boots, hats and coats. You never know when you may get soaked. Also make sure that you have some decent blankets, quilts, sleeping bags and mattresses as spares in your home.
This completes the minimum of what we need to live because we could not cook our food and still live. It would be tough but possible.