Well, if you have the money, you can buy a big generator to power all your house, or get a small one to power just your fish tanks.
But to the regular hobbyist the best option is to get one of those battery powered air pumps, so you can supply oxygen to your tank and keep your livestock alive, you can find one here:
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=8120&Nty=1&Ntx=mode+matcha llpartial&Ntk=All&N=2004&Ntt=battery%20pump&Np=1
If you live in a very cold area, heating also maybe an issue. You can try getting an UPS (uninterruptible power supply), the ones that come for computers and home appliances, you can hook your heater to that UPS unit and get 2-10 hours of heating, depending of the wattage of the UPS you bought.