He took 2 liters of fluids with him, which worked in the below freezing temperatures, but I'd want a lot more than that for a summer walk. I'd suggest he try it again in July or August.

I don't know what his disaster scenario is. In the San Francisco Bay Area, walking home after an earthquake is very likely. Most roads on the peninsula have overpasses or are overpasses, and collapses are likely. As a corollary, this means don't bet on getting a room anywhere. Don't bet on buying a meal if the power is out.

Don't bet on a convenient time of day for the earthquake, so have glow sticks and reflective tape - but don't bet on people having lights to reflect off the tape if they're on bikes. A letter carrier I know was run down by a guy on a bike - he wasn't hospitalized, but he was unable to work for several days and thought his spleen was ruptured. If you're hit by someone on a bike, you'll be hurt.

I would absolutely take a camera. If this is the Big One, having photographs to document the conditions will be very nice for later years and generations. Notice how his photos and comments about them added to the story? "Luke! Use the camera!"