luckily i live in an area where we dont have too many disasters. I always have a few tins of veg in my cupboards that i could use in emergency's - carrots and the like. With regards to meat, i breed my own dubia and i always have mice in the freezer for my snake.
With regards to heating i have a few reusable hand warmers that i just boil in hot water to reuse. I always use them when transporting a reptile. I also have a spare hot water bottle and battery powered kettle that i use for extra heat. I get a lot of power cuts at the moment since there's near by electricity works going on. Though i've had 2 this week just due to some fuses blowing in the system - took 4 hours to fix each time! My snake had just been fed so heat was essential, especially since hes such a fussy eater and had been refusing feeds making this feed important! I filled a hot water bottle, affixed it to the side of the glass tank and he huddled up next to it. I put cold water in with the boiling until it was the kind of temperature you can comfortably hold to your skin, just to be safe. I suppose something like that could help a beardie stay warm.
As long as the rooms fairly warm i suppose they could go without heat/lights a few days. Hige's been getting ready to brumnate so he'd cope fairly well without any for a while.