Sketchbooks
I almost always have a 4 x 6 sketchbook with me. Here are some examples, in no particular order. They often lead the paintings, or are sketches of paintings in progress. Many of the images of San Francisco bars are from Tunnel Top, Elbo Room, Vesuvio, Hemlock ... and plenty others.
The numbers are the approximate month-year-page. Each sketchbook results in approximately 17 images.