If you go to battery1234.com and scroll down to How to Power Your House from Your Car with an Inverter you can learn how a fairly cheap DC/AC converter can be hooked up to your car battery to provide emergency power to your house. Depending on your car's alternator, you can get up to 1500-2000W of power, which is enough to run a fridge or freezer. You car acts as the generator and you can run for a loooong time on a full tank. That would allow you to get up and running quickly if you lose power.
You could also invest in a small battery bank and run your incubator off that while it's constantly recharged from your wall socket. If you lose power, it'll keep going. Two good sized deep cell batteries would probably keep you running for two days. It's more expensive than an inverter running off your car, but you don't have to be there to switch the power over. Depending on the value of your hatching eggs, it could be worth while. Also, if you sell your chicks or chickens, you should be able to deduct the cost of either method.