Here's a good page on what to keep in an emergency kit:
http://www.sff.net/people/doylemacdonald/emerg_kit.htm
Yes, you can buy emergency foodstuffs: eg., very high-calorie vitamin-enriched food bars that don't make you thirsty (and that come with a 5-year shelf life); little boxes of water that have a 5-year shelf life and can withstand temperature extremes.
I keep UHT milk in the cupboard. And bottled water too.
If you google "emergency kit" or something similar, you'll come up with all kinds of commerical sites selling supplies. Also, the Red Cross sells emergency kits that include a 3-day food supply (for 2 people or 4 people) along with first aid stuff and other emergency items.
My husband thinks I'm nuts (and back in 1999 I thought those Y2K people were a bit nuts), but I am buying one of those Red Cross emergency kits.