There are a lot of threads on this if you want to look them up.
But otherwise think:
Light
Warmth
Cooking
Power
Phone.
Light:
What do you have already?torches, lanterns, those outdoor solar lights, battery operated fairy lights batteries. Those battery operated spot lights. (next to the fuse box)
Recommend a head torch.
Also a solar lantern as they recharge during the day. (I have one each person but only just got the last one on the slow boat from China).
Warmth:
Hats, scarves, wrist warmers, woolly socks, (layers increasing in size, fresh ones for bed) thermal base layer (Marino if you can afford it) (cheap ones are very thin and I am seeing holes in one set) woolly jumpers.
Plenty of blankets/duvets for the bed /sofa.
Warm slippers.
Rechargeable hand warmers,
Flasks for hot water you've heated up or acquired from outside the blackout zone from a mate etc.
Cuddle up together, if it's really beast from the east cold, in the smallest warmest room, or camp indoors under the dining room table / bunk bed covered with duvet covers.
Long term: insulate your loft, draught proof, get thick lined curtains. Etc. .
.