Hi guys I'm on the East Coast of the US and we just went thru a pretty big blizzard. I was worried about the power going out and not being able to keep my sweet Hammie warm; luckily we never lost power but I stocked up on these Hot Hand body warmers just in case. They're these little packs that you shake for a few minutes and they give off heat for up to 12 hours. I used them before when our furnace went out and they worked great! I just laid them against the side of Hammie's tank (DO NOT place inside the cage- even if your fur baby isn't a chewer the contents may leak and cause them harm) and swapped them out when needed. If you shake them periodically they last even longer. You can find them in the sporting goods section of all the major stores, like Kmart, Walmart, Target, etc.
Here is a link on Amazon so you know what they look like:
Amazon.com : HotHands Hand Warmers : Sports & Outdoors