Heck, that happens, but not on a vast scale, every year to some area around here. My power was off for 21 hours, and most was back within 48 hours. Things were still screwed up for days afterwards. That's why the "three day supply" is about the same as the government's advice on "plastic sheeting and duct tape". Better than nothing, but not much.
A one-week supply of drinking water and food is not much harder to put together than three days. It's very nice, however, to have "flushing water" too. I forgot to thank God for allowing us to have full water pressure, even though we were ordered to boil it before consumption (which turns out was not really necessary). Some areas lost water pressure, and were in a real world of hurt.
As long as you have water for drinking and flushing, your survival is already much easier and more comfortable.
EEEEEEKKKK!!!!