If the worst case scenario is The Big Shake, then it seems to me the biggest worries are egress from a damaged building and access to water.

Egress means tools. Indestructible flat prybar, at least 15" and with enough mass to chop/hammer. 10" Vise Grip with wire cutter. A hatchet likely won't be allowed for safety reasons.

Water: won't fit in a shoebox. When pressure is lost, where can residual treated water be found? I don't know the answer. I suspect raw water in CA may be pretty heavily loaded with agricultural chemical runoff, and worse after a shake.

Also not in shoebox, but ideal: a bug out location within walking distance, to known parties who have resources and can be trusted.

Kudos to papa for worrying. :-)