Do water changes fairly frequently until the power comes back on - there's some bacteria on any surface in the tank, but most of it is in the filter, which isn't running now. If it's under 24 hours, you shouldn't have major die off in the biofilter.
I keep my tanks on uninturruptible power supplies, which are usually sold for computers. They'll keep a PC and monitor running for 30 minutes to an hour depending on model, but my tanks have gone for several hours on them before.
Somebody in a similar threat suggested a car battery and a wall plug adapter like they sell in automotive stores. Probably a cheaper option, but remember to keep the battery charged.