If your power is out, absolutely do not feed!!! Usually we have some warning that a storm is approaching. If so- do not feed!
The 40 hour heat packs work well. You can put one in a deli cup, with holes, and put that in with your snake. You can also put your snake in a snake bag (test the corners first!!!) and carry it under your shirt.
If it's cold long enough that you have to leave, do not leave your animals behind. You can pack snakes in snake bags, then in Sterilites, then in reusable grocery bags, and take them with you.