Hand warmers can serve as emergency heat pads. They can be placed under tanks or under carriers. Be careful when using them because they can get very hot. Monitor cage and surface temps carefully. Keep in mind that most hand warmers get hotter when exposed to more air. DO NOT PLACE DIRECTLY IN TANK!
If you have to move your animals to a warmer location or a place with power, you want to make sure you have enough totes to carry all of them safely. This picture shows some of my feed containers and critter keepers. Plastic totes that are not clear are better (darkness reduces stress and thicker, "weather resistant" totes may hold heat better), but clear totes can be used. It may be handy to keep some extra substrate around so that you can easily add some to the totes. Snake bags are great for transporting snakes. Pillow cases can also be used (just make sure you tie them up well)! Cat/dog crates and carriers are another possible way to transport your bigger herps. I brought home Gary the ball in a soft-sided animal carrier (much to the amusement of my coworker). Just a side note: I would strongly caution against adding anything (like cage furniture) to the totes because they can move during transport and hurt your critters.
Try to keep the room warm
Keep all windows and doors shut. Keep blinds and curtains closed. If you are preparing for a storm well ahead of time, you will want to check for and fix any drafts. We were very fortunate because at the beginning of winter, we bought a kit to fix our drafty window in our reptile room (this helped all winter long, not just during the storm)! If you have a "reptile room" or a warmer room, you can use objects (like pillows and blankets) at the base of the door to block it from larger or colder rooms. I highly suggest moving all of your herps into the warmest room in the house. Another thing you can do is blast the heater when the power comes back on. If the power comes back, don't assume it will stay. Turn the heater up as soon as possible.
Try to stay with your animals
Keep an eye on your critters! A local zoo lost all but one of their giant salamanders because no one was there to monitor the aquarium temperature. When the power came back on, the chiller failed to turn on with the pump, and the water was accidentally heated to over 80 degrees! The poor salamanders (which would have happily survived the extreme cold of the winter storm had the power outage continued) overheated. You can avoid problems like this by monitoring your animals and their cage temperatures closely. Don't assume that because you have an animal that can tolerate cold, that he does not require monitoring. Power outages can cause all sorts of problems.
Have a Plan
The most important thing is to have a plan. I talked with a few of my friends after the power outage and many of them were very panicked about their animals during the storm. One of my coworkers had to sleep with her bearded dragon to keep him warm because she had no power and no emergency plan! Decide what you would do in the event of an emergency. Where would you go if your home gets too cold? I have a friend with a powerful generator, but not everyone does. Do you have enough totes to transport all animals safely? Where are your emergency supplies? Keep in mind that while many herps are hardy and can go a very long time without food and water, very few of them can tolerate extreme cold. And if you have multiple animals, some of the may tolerate cold better than others. Decide which animals will need to be moved and when.
So there is my post about cold weather emergencies. It may be a really long time before the next winter storm, but you can use all that time to prepare :)