Battery-powered air pumps are cheap and available at just about fishing tackle shop. They work well, even for extended periods, if you have enough batteries.
Failing that...just get a couple empty, clean plastic milk jugs or similar. Punch a small hole or two near the bottom of them, fill with tank water, and then stand them on top of the tank such that the water dribbles out of the holes and back into the tank. Re-fill as needed. Experiment with hole size and number, and with the top on or off, to get the flow rate you think is best. This keeps a constant low-level aeration going on, which is much better than periodically dipping water out manually and pouring it back in; easier too.
The more crowded your tank, the more important this becomes. Lots of tanks don't need aeration at all...either during emergencies, or simply for normal maintenance for many species. If my power went out, I would likely put on battery pumps for only two tanks; I know for a fact that the rest will be just fine, indefinitely, without any. Discontinue or drastically reduce feeding, maintain a good water change schedule (none of this "20% once a month" nonsense) and learn to relax.
We had a pretty decent power outage here once. First thing I always do is remove all the tops (surface area is your best friend). Then I duck tape the battery packs near the top frame and let the airstones just hang near the surface for agitation. You can go with slightly bigger airstones since the kit ones are kinda wimpy (I used splitters for the 225) The hoses tend to be really short like 3 ft, but in this instance that works in your favor. You want the stones near the top not the bottom. Adjust the hose length for 'maximum bubblage.'
For bigger tanks a power box is good. Get one with multiple type outlets. They take around a day to charge up in advance but you can have one always ready. If you really wanna get fancy solar panels go with a lot of the models. But the panels take a day or two to charge.
