The two main items you must provide are food and water. FEMA has determined that a family of four needs a minimum of 28 gallons of water for one week - 53 2-liter soda bottles. That figure assumes some frugality of usage - mostly for drinking - and that users are staying in one location with minimum activity. More activity by any individual may require more water consumption.
A few years ago DH had to do something with water pipes/well/something or other and said water would be off for several hours shortly. So I filled up every single available bucket/jar/bowl/pot etc with water as fast as I could. Turned out he couldn't get water back on for at least 1 1/2 days IIRC. We were totally frugal, cooked minimally, washed very few dishes, re-used water (first for hands and face, then same water for ickier stuff, finally for flushing toilet), took sponge baths.
I figured out how much water 2 people used in less than 2 days (or thereabouts) for very minimal water use and it was around 42 gallons.
FEMA's pathetically minimal water storage means they can drink and use a few drops on their hands and face and that's about it. Barely any washing, bathing, flushing toilets, cooking etc. They should make it clear that people should store much more water than that.
(I posted a reply but I don't see it... Will redo...)
Yes. I plead brevity for the sake of an introduction; I just said 'frugal' and enough for drinking. Water is critical! The more the better. I like that bladder that lays in the bathtub. It says 'up to 100 gallons' but that seems a bit optimistic. Folded it is small and takes no space for storage, but expands nicely. It says it is made of 'food grade plastic', an important consideration.