Glenn Reynolds had a post today reminding people about the importance of keeping at least a few gallons of water stored against emergencies because of Boston’s recent water problems. That is great advice. You can not assume that your utilities will work without hiccup or you can always head to the local store to buy a jug. I am not saying to bunker down and prepare for the Armageddon, but you should have enough supplies to last for at least a few days. That is to say long enough for the services to be restored or for far flung help to arrive.
I will add to the advice on water that you should also have some food that does not requires any electronic assisted preparation. You can not microwave a meal if the power is out. Likewise, it would be pretty awful if you could not open your stored canned food because your electric can opener ran out of juice (power).
If canned food with a manual can opener is not your thing, you can buy a few bags of beef jerky and store it with the water. Keeping a glass jar of honey in there as well is a good idea because it will never spoil. Keeping a keg or mini keg around (yes, beer) can also be a good idea because it too will never go bad and is basically liquefied bread. One quick caveat about the 'never go bad' thing for the beer; it will never be dangerous to drink though the taste may shift to the more unpleasant. Still, if the choice is between off-tasting beer and nothing you may convince yourself the beer tastes even better then usual.
You should consider rotating your emergency food. Beef jerky should be good for at least a year. If you do not want to waist food or be nervous about your emergency stash having expired, then eat a bag replacing it with a new one every 'X' months. Your equations is the assumed storage length divided by the number of bags you have. The same goes for all of your food stores and keg of beer, though the beer may be more enjoyable then the rest.
While not wanting to turn this post into a book on disaster preparedness, I will end by adding that having a way of generating power is important. It can be something as simple as a hand crank generator with a few plugs so you can recharge your radio to listen for emergency broadcasts, recharge your phone to call for help, or charge your mp3 player to keep you from going stir crazy. You do not need a generator capable of keeping all the lights in your house on, though if you can afford it that would not be a bad thing to have, just something to keep a flashlight charge which will make you feel much better when night falls.