I vote plan for a week. Clearly for every disaster, the swath of destruciton is critical for asessing the impact. A tornado can take out a city block or a whole town...and everything in between. Out here in California earthquakes can knock down a few or many building ....destroy small bridges ..no bridges or many major arterial freeway connections.
My personal goal is to be prepared for a week ... and then extend and build on that. Sheltering in place I can do that now. But I';m not quite organized enough to get all that stuff into a car in short order (less than an hour) and move it to some undisclosed location when the powers that be tell me to evacuate for a brush fire. Thankfully ...I'm urban enough for that to be less of a threat than other scenarios. But still, one day I want to be able to do pitch all my supplies in my truck and hoof it for greener pastures.
By the way ... its 7.48 gallons per cubic foot...and water weighs about 8 lbs per gallon. Unfortunately, with containers that are durable enough to be handled a lot you'll need more space than one cubic foot for 7.48 gallons. I like 2.5 gal containers 'cuz they are eaier to handle than 5 gal containers...but good ones are pricey....and moving a large amount of water when bugging out is heavy ....bringing adequate water in a bug-out scenario is one of my concerns yet to be fully resolved.