Due to the fact that during the Winter, my town is prone to once-a-month blackouts, I was in the market for some battery-operated/rechargable/non-outlet powered aquarium filters and water pumps, and even lights.
How long is your power out? Your fish would do fine for several days or longer with out the filter or pump. It would be the heater I would worry about. Are these power outages year around or just in the winter?
Thyra is correct, its the temp of the tank that is important. You can always stir the water every now and then with a large slotted serving spoon to generate oxygen. I would be looking for a propane or other type heater for the area/room the tank is in.