What is the best use of free time on the road?

I'm starting a new job in outside sales. It will be long days on occasion that can last from 8am-10pm. The problem is that I will have blocks of times in unfamiliar (even rural) areas. This could be anywhere from 1-5 hours of "sitting" until my next appointment. With gas prices so high, going home would not be an option. I would ideally like to lose weight but I'm not a runner and with the high humidity in this state I don't want to go to my next appointment looking like I just ran a marathon. Does anyone have any suggestions on how I can be productive with my time or get some exercise in?