What goes around comes around. I remember thinking about this at a time when the USA and USSR were glowering at each other across the globe. We had a caravan standing in the drive which was usually stocked with enough basics for a few days away - water, bedding, tins, first-aid stuff - but it wouldn't have kept a family going for very long.
I also remember the Anderson shelter with the garden chairs, tins of beans, bottles of water, books and jigsaws, and the bucket in the corner. It didn't get much use - there was a communal shelter quite near which we went to a few times, but thank God not often.
Far more than five -
Water and water-treatment tablets
Chemical toilet
Tinned food and vitamin tablets
Warm and waterproof clothes and boots
Bedding
Wind-up torches and radios.
LED lights and spare batteries.
Matches
Lots of poly bags of various sizes
Books, paper, pens and pencils
String
And for when you emerge -
Weapons to defend your patch from usurpers
Vegetable seeds to start from scratch
Instruction books for building, farming, medecine, and any other subject you can lay hands on.