Thanks for the help! I hadn't thought of a tornado, though I suppose it's an obvious cause of an outage.

I had been curious about grocery stores, so this post's been good for that too. I was at a grocery store when the power went out once and all the lights were out, none of the registers worked, but the freezers could stay on for another 8 hours or something like that. OT, that's probably a smart idea for any grocery store- one time my friend accidentally turned the freezers off at the store where he worked, and they lost almost $10k in frozen foods.