Instant mash, with sufficient milk in the liquid mix (and sufficient liquid) a good knob of butter, and possibly a teaspoon of grainy mustard, is actually very good.
Long life shelf-stable milk is really handy (most milk sold here is like that, has about 4 months life normally so I usually have a couple of cartons in for when I cannot find proper fresh milk…I’m not in UK).
Nasi goreng - basically cold cooked rice fried up with a tin of tuna, tin of corn, garlic, onion, some mild curry powder - in normal times, we add mushrooms, peppers, frozen peas and frozen prawns but the storecupboard version is fine for something hot and tasty.
Paella type rice dish using stock, rice, saffron, onion, garlic, some tomato concentrate, tin of mussels, olives from a jar, roasted peppers from a jar….
Tinned clams with pasta, garlic, dash olive oil and squeeze of lemon.
Confit duck from a tin with potatoes roasted in the duck fat.
I can also get cassoulet in a tin here, and ratatouille in jars. And shelf-stable chorizo and other salamis. Jars of sun-dried tomatoes can add some flavour too. Jars or tins of both green and black olives. And tinned veggies like French beans, asparagus, mushrooms or the normal different varieties of beans and lentils and chickpeas. Or the Chinese style cans of veggies like water chestnuts, baby corn, bamboo shoots and bean sprouts. Don’t forget root veg like carrots, parsnips, swede, and brassicas like cabbage and Brussels sprouts which generally last a good while without refrigeration.
If you look carefully, there are lots of things you can find in a regular supermarket, or a few bits and pieces from delis that can be really useful, that may not get a lot of regular use but could be really helpful if the power was gone once you’ve used up the “likely to go off quickly” items from the fridge.