Your preparedness plan will depend on how many snakes you have and how much available space you have. Someone living in an apartment with just a snake or two won't have the same needs as someone in a house who has a herp room and 100 snakes in a rack/tub setup.
If you just have one or two smallish critters, then secure each snake in a pillowcase or snake bag, and put that under your shirt next to your skin to keep the snake warm. Congrats - you'll have a bouncing BP baby bump!
If you have a few snakes you can put them into their own bags, load them all up in one tub or an insulated box with supplemental heat, put them in a warm car, and they'll be fine until they reach their destination - assuming you have somewhere to take them.
Someone planning to stay in place will need a generator. I wouldn't worry about running all of the t-stats and belly heat; in fact, a digital t-stat may not do well on dirty generator power. Just heat the herp room to the low/mid-80's F for a few days using a space heater.
Harbor Freight has several generators on sale right now; the 7KW Predator model is a steal IMO at $550 - and if I didn't already have two generators I'd be jumping on that one. Note that the larger workhorse models tend to be quite loud, so if you get one you may need to offer to let the neighbors run an extension cord to it in exchange for gas, if you want to maintain neighborly relations. If you plan to run it all the time, including all night, someone in the house needs to be awake at all times to make sure it doesn't walk away.