For blackouts that last less than a day one or two 10Ah+ power banks with a flashlight built-in should be enough.
Remember to dress well so you won't freeze
An EV is a pretty good powerbank if one needs a car anyway.
That's a bit too steep just for a powerbank ;-)
If you have a gasoline car you can charge in that from the starter battery.
A starter battery is about 1kWh.
Or just keep a lead acid battery around charged up and connect a ciggarette lighter socket to it.
I was specifically curious about dedicated powerbanks. This discussion got sidetracked to cars.
This one isn't intended for cars, but apparently is powerful enough to be able to recharge one, and popular youtuber Bitluni modified it to do just that.