Background: I live on North Oakland, next to Berkeley, in the Rockridge section. Urban, detached 2 bedroom house about 100 years old.
We bolted down our house, fully reinforced the stemwalls, and installed shearwalls. For our little 2-bedroom bungalow in Oakland, this set us back around $20,000. Earthquake insurance seemed outrageous (around $2,500/year, with very limited benefits). Along with the earthquake retrofit, we set aside a few cases of food & twenty 5-gallon jugs of water. A 2Kw Honda generator. Radio, flashlights, FRS walkie-talkies, etc. Small amount of medical stuff.
Yes, I have onsite and offsite backups (that's easy); the real problem would be connectivity after a quake. There's probably a hundred telephone poles between my house and the central office.
Some challenges: Keeping food & water fresh is a problem - cans get rusty as water condenses on cold surfaces. Some camping food goes bad. MRI rations taste, well, horrible. We should replace water & food annually, and generally forget to. (We discovered diapers in our earthquake stash, left over from when our college kids were infants)
Storing gasoline for the generator is a problem. I'm told that gasoline gets stale after a few months (is this true, or an urban legend?). It's a pain to lug a 3 gallon gas can around, and it's not something I want under my house. (I store it in a shed, where it's out of sight & out of mind - so I rarely refresh it. Is there a small, 5 or 10 gallon under-ground gasoline storage tank?). I should start and exercise the generator every month; it's more like every two years or so. Our experience in the 1989 quake was that gas stations can't pump after an earthquake (no power).
Our neighborhood's quake group (the Oakland - Rockridge Shakers) meets every summer, and the earthquake drills have been quite useful - we've had several fun practice sessions, where we hunt for human dummies hidden around the neighborhood, search for downed wires, and practice using walkie-talkies. Afterwards, it's a block party, and we compare notes while sharing lunch.
My home business, Acme Klein Bottles, lost two glass Klein bottles in last night's quake. Both fell off a shelf and shattered on the floor. Good lesson: keep my glassware stored down low, with holders to prevent boxes from shifting. Since most of my glass Klein bottles are stored under our house; a major local temblor that destroyed the house would also wipe out the business.