For those who live in a flat without gas...and don't want to store camping gas inside)
Insulate well. (Loft if you have one, loft hatch, thick curtains and blinds, door curtain, )
Lots of flasks/food flasks. Make added insulation bags for them from kids old coats.
Hand warmers. The gel ones you press a button on and can be recharged by boiling . First aid press button cooling packs for summer if your place gets way too hot . (Not rechargeable)
High calorie food that can be eaten cold. Chocolate. Biscuits. Crackers.
Blankets, gloves, phone gloves, wrist warmers, leg warmers, woolly socks, hats, slippers.
Power banks. Lots.
Solar lanterns. At least one per person. Wind up lanterns. Get a spare or two for downstairs neighbours...them using candles can effect you. (Two large fires in the local city flats recently)
Fire blankets and fire extinguishers.
A grab bag for sleeping at the local rest centre. (What would you need if you were to sleep at a local church hall for example?) Money pouch underclothes? ( I slept on the hospital floor on a mattress for three days using our prepared hospital bag. See those threads for ideas )
If you have storage away from the flats and outdoor space, then disposable BBQ and stand or camping stove will be useful. Only use outside and not on a balcony. Have some pans that will go on the BBQ to heat simple food.
(Tinned curry, plus tinned veg stirred in is good)
If you have a sunny window, try a solar kettle or solar oven on suitable surfaces.
Friends in other areas and transport to them. (Petrol in your car, bus fare cash, flasks, chargers to top up your phone). Insulated bags.
A deliveroo/just eat account and money to pay for it if the power cut is only local. (Eg some people stayed in their flats in one tower block after the water from firefighting knocked out the blocks electricity supply)
Indoor camping. Get together in your warmest room and sleep there. You can make and indoor tent with table ,chairs, sheets, blankets or real tent if it's really cold. Keep body warmth in a smaller space.