Preparation is critical, and it comes in two parts. One is the plan, and the other is the necessary supplies after the earthquake. In the plan, there should be a what to do when the earthquake strikes at home or elsewhere, as well as what to do after the earthquake. The plan should include contacting your family if you are not all in one location. A sitrep should be completed, and the rest of the actions can be executed.
What you will need for supplies would be, food, water, power for devices (cell phone, GMRS or ham radios, flashlight and headlamps, GPS, etc.), and if you are not in your designated location, what you will need to get there. This is where a Get Home bag or a Go bag is important. As far as food, you should have food to feed everyone for 2 week minimum, and water for everyone for 2 week minimum based on the CDC recommendations.
Water requirement per person based on the CDC website is 1 gallon per day per person and should have 2 weeks of water. My recommendation is 3.5 gallons per day per person. Most people need to drink water to survive, and in many cases, you need water to prepare meals (like camping food), and don’t forget your pets. If you don’t use the 3.5 gallons per day per person, it will last you longer than 1 week. So, if you have a family of 4, you should have 98 gallons of drinking water available (this is based on my 1 week minimum). Having more will be helpful, but if you can’t store 98 gallons of water, have at least 56 gallons (based on the CDC calculation of 1 gallon per person per day for 2 weeks) and ration. Remember, water is more important than food.