I keep a case of MRE's and 5 gallons of potable water at all times. Ya have to change the stuff out every once in a while, but being prepared is worth it. Next year I plan on purchasing a couple of pistols and a shotgun, again just in case.
You know that if you drain it out a little every once and a while, your hot water tank is a good source of backup water. I'll save you the hassle though. Before you drain it, get one of those caps for a garden hose. The spigots on water heaters are real cheap and will leak.