For me it depends on what we negotiated for a fair in part. If we stop for food, I like to include the driver for a meal and that never is too much and fun to chat with the driver and know that he (wanted to also say she but never had a female driver as I think back and do not recall any...interesting) ensures we understand the runnings/protocol if needed. The meal can simply be a boxed lunch..oh so good and great value. $10-$20 US is my cash tip. Have great fun and that begins with your ride.