My wife and I talked about emergency preparedness the other day. She wanted to buy a kit from Costco, and I pointed out that with a little creativity we already have a lot of what we need.
Water: first off, our R.O. unit has a 2 gallon tank. Each of our toilets has 1.6 gallons in the tank. We have a propane BBQ and at least one tank of propane on hand so we could start boiling water the stored water runs out. If the muni water system isn't delivering anything at all, there's a creek nearby. And we have a ceramic purifier filter (for backpacking) that we could use in a pinch.
Food: At any given time there's at least 2 weeks' worth of dry and canned goods in our pantry. We shop at Costco and naturally stock up.
Shelter / warmth: We have a couple of tents, tarps, sleeping bags, and lots of blankets and sheets.
First aid: We already have a first aid kit.
Communications: We have a hand-crank radio, and a solar battery / cell phone charger.
Defence: In my mind, the most important item after water. We have weapons and ammunition.