You can get hand warmers from Walmart and set in the tank but you must cover them w/ a dish towel / towel because they get very hot --- I think they make them like 4 and 6 hr warmers -- some others on here might have some more ideas @CooperDragon
I don't know if those are the same- those could be better but I have seen them the hand warmers posted on here I would check into both of them and go from there
Run your car and use the heater to keep your beardie warm until the power is back on. DO NOT RUN YOUR IN A CLOSED UP GARAGE!!! Carbon monoxide will make you all sick at a minimum and could kill you all if exposed for to long.
The reptile shipping heat packs are very good. I always have some on hand. They don't get hot enough to burn, and they run for quite a long time. I've used them on camping trips and they've stayed warm for 3 days just as the packaging indicates. They're worth having - just double check the expiration dates and use them up and replace them as needed.
Another good idea, but more expensive, is to have a battery backup for the lights (or just one heat light). These are typically designed for computers or servers but will keep a low wattage heat emitter going for a little while. Due to their limited run time, they're best suited for short outages of up to a few hours.