Depends on how many animals you have
One or two snakes - Heat Packs (Those meant for shipping not hand warmers) or hot water bottles.
A larger collection, generator and/or http://www.walmart.com/ip/14710768?a...l5=pla&veh=sem
I have both the generator is mainly to allow us to have our fridge going and lights and my incubator and the buddy heater is to allow the snake room to remain at an ambient temp of 78 degrees.
A little tip though the worse time to buy either of those is when there is a threat of big powerful storm, chances how they'll be hard to find.