This is an interesting topic as I have considered this, quite often. I live in a place where winters can be harsh and worry about losing my animals if I lost power for any more than a couple of hours.
I think the first obvious thing is to have a generator. Of course, this is not possible for everyone.
For me, I have several appropriately sized insulated animal shipping boxes with heat pads at the ready. If I lose power, I gather up all the animals and put them in heated boxes until power is restored.
If the power outage is more than 24 hours, I panic!!!!