Here is my theory as a lifetime native Californian...yet for some reason its not a popular one...

I have rolled through several big ones and never once had an injury nor damage. Also have never needed so much as a single supply.

Now here is my one and only helpful earthquake preparenedness tip... Get to know your neighbors. If theres aarge enough quake that you would need any of those stupid supply kits, trust me they will be buried in a pile of rubble and useless to you any ways. Getting to know your neighbor is helpful because when the FD finally shows up days later it may be too late. Your neighbors will be the first responders to you and your family. You will be there for each other to turn off gas/water mains and to pull each other out of whats left of your home. Fail this step and to me thats the entire plan. Your first aid kit and water bottles will be garbage in the rubble.

But alas bring on the downvotes cause people don’t like hearing the truth.