One of the big fears of aquarium owners is an extended power failure. An aquarium is always stocked well above natural fish concentration, and depends heavily on the life support - the aquarium pump and heater. When you loose power, it's just a matter of time before the loss of aeration and heat will start stressing and killing your stock.
I was browsing the Harbor Freight website, after reordering their catalog after twice with no success, and stumbled upon a live bait aerator. This would be a perfect backup aquarium pump if the power cut out. Granted, buying anything from Harbor Freight is a hit, or miss, or miss proposition, but $5 seems acceptable for something that may or may not work, and that you may or may not ever use. Just make sure to have a D cell ready, or it'll do you no good unless you pull a MacGyver with a AA and a paper clip.