Battery powered backups, big water change beforehand, light feeding, keeps lights on planted tanks (plants only provide oxygen when photosynthesiszing, otherwise they use it), insulate tank with Styrofoam (not completely over the top, though, and be sure to leave enough gaps for observation), and be prepared for your fish to react poorly to the pressure change. Fish are often nervous during big storms, and any particularly anxious or dash-prone fish (pacu, gar, silver dollars, etc) should have each end of their tank cushioned with something like a big bunch of plastic plants. That helps keep them from breaking their skulls open.
You can often get some fairly long-lived and powerful battery-powered air pumps at anywhere that sells bait and fishing supplies- they're for bait buckets, but they work for aquariums. Some are a bit loud, but most can be muffled with a towel.