Use long waits as an opportunity to improve your bass playing instead of diddling with your cell phone. Take sheet music to read/ study/ memorize. Without a bass in your hands, it frees you up to understand and memorize. Did this today on 1 1/2 hr wait for new tires. Airports/ flights are good too.
When I used to drive long distances for work, I would "play along" with the radio in my mind. I remember a few times when I would think an improper note, and realized it. That's when I knew I had my fretboard and theory down.