Battery powered air pumps from walmart or a generator. If you don't have either and can't get them, put your filter media in the main part of the tank, stop feeding everything except fry, and do small water changes if possible to replenish oxygen or stir the water around. If you have some big buckets, fill them up with half tank water and half new water, place some filter media in, and stick some of the fish in there to lower the oxygen usage in the main tank. If you have live plants be sure to provide them with lots of light from a strong flashlight if possible so you have a little more oxygen. Every bit counts, and turning off the lights makes plants perform cell respiration, which uses oxygen and puts out CO2. Also, the rainwater would be good to use for water changes if you collect from an area where it doesn't run off anything, just collects into a bucket sitting on your driveway or something like that. The water would be chock full of oxygen due to falling through the air for a while.