2 up 2 down. Have you any space under the stairs?
Options:
Boxes in the loft space.
Boxes in the shed - cans would be ok out there.
Boxes under beds.
Shelving in main living space repurposed - put books or ornaments into loft space.
We generally have more of things the family including the children would normally eat. I try to stock up on non perishable items and some things that would be easy to heat from a can or packet rather than cook from scratch. Staples such as pasta, rice, dried beans and pulses etc. Milk powder or long life milk cartons. Tins of soup, chilli, curry, sauces, tomatoes, pulses and tinned meats.
3 months or more is ideal, but anything is better than nothing.
Other things that might be useful:
Some cash in case ATM machines and card payment services not able to operate.
A water filter in case water supplies affected by power outages, you can get personal straw type water filters like LifeStraw and WaterDrop via camping supplies.
Rechargeable camping lanterns
Camping stove with butane canisters for cooking
Hot water bottles to fill to keep warm
Kettle that can be used to boil water on camping stove.