There's obviously not a huge amount you can do, but here are two things.
First, don't feed it tonight. Let the filter remove any ammonia before it gets switched off!
Second, fill a couple of buckets with water ready to do water changes if necessary. What kills fish isn't drops in temperature for a day or two, but declining water quality and insufficient oxygen. Water changes will help here. If you can replace 50% of the water at a moment's notice, you'll have a good backup plan.
It's also worth mentioning that if the power goes out you should unplug any canister filters and remove the biological media to an open basin of water so that the bacteria can "breathe". The last thing you want is a bunch of dying bacteria connected to your aquarium, using up oxygen and pushing out ammonia.
Cheers, Neale