One of those questions thats bound to get the same few answers. Its really something you should consider based upon where you live, how long a typical outage lasts for you and what size tank/tanks you have to support. Theres really no one size fits all answer.
For me and my two tanks a few battery backup air stones and car battery inverter as a worst case are all I need. I generally only lose power once or twice a year for under an hour though. We have our own local utility in town so repairs are made very quickly. If I was one town over or lived in a place that could be out for days I’d take very different precautions.
At the minimum get the airator battery boxes they sell for keeping bait alive and stock up on batteries for it. I lasted an outage that was almost a week during this summer doing that. For the heat I have a space blanket I can throw over the tank to try and insulate it.