Preparedness experts recommend that residents of disaster-prone areas have supplies available to remain self-sufficient in the days and weeks after an event like a megaquake.
The supplies any one person needs for a disaster may vary, depending on the type of damage done and life circumstances, such as having a medical condition or needing to care for a child.
The American Red Cross does recommend a few basic items for everyone, however:

In the event of a natural disaster, each household should have one gallon of purified water, per person, per day, stored. It's recommended that each family have two weeks worth of water at the minimum. For a family of four, that equates to 56 gallons of water.
Alan Sylvestre / OPB