We have a camping stove, gas BBQ and a fire pit so I'm not so worried about how to heat food but I haven't bought too much that would need lots of water to cook it. I'm also only buying things we will actually use so nothing gets wasted.
Breakfasts - cereal and long life oat milk (I don't like UHT cow's milk but the Plenish milk that's just oats and water is fine. It would also do as a drink in an emergency.) Boxes of flapjacks or similar oaty breakfast bars.
Lunches/Dinners - we always keep plenty of cheese, apples, pears and satsumas in the fridge. These would last for days if the fridge went off. Similarly we always keep a loaf of bread and a carton of milk in the freezer so would prioritise eating that if we had a long lasting power cut. Eggs and potatoes last a long time too so always have plenty of those.
Wraps or rye bread also often have very long dates on them so we always have a couple of packs of each in the cupboard. With peanut butter that would fill us up well.
Tinned tuna, microwave rice, baked beans, mixed beans, jars of pesto, tinned soup. You can also cook small pasta like orzo directly in tinned tomatoes or jarred pasta sauce so you wouldn't need to use water there which may be helpful. You can buy chorizo in Lidl that doesn't need refrigerating if you want some meat.
Snacks - crackers with peanut butter, crisps, biscuits, dried fruit, nuts, tinned fruit and custard.
Other stuff - bottled water, vodka (for drinking and for sanitising if necessary!), torches, power banks, candles, matches, toilet roll, bin liners, battery radio and spare batteries, water sanitising tablets and baby wipes for keeping clean and preserving water if it goes off.
I think we'd be fine for a few days eating cereal with long life milk and dried fruit for breakfast, cheese or peanut butter on crackers for lunches or heating up a tin of soup. Then tuna, pesto and mixed bean salad or frying up eggs, potatoes and chorizo on the camping stove for dinners.
With crisps, booze and some biscuits for morale I'm sure we'd be ok.