In the passenger seat (or, the driver's seat, for that matter), as long as you lock your door, you can get somewhat comfortable.
As you experienced folks know, someone opening the door when you are sleeping on it is a shocking experience, to say the least.
It's true about having something to do, though. At the one posting in Amherst, NY, I used to call in to a local radio station and talk on the air all the time (we were in the parking lot of a hotel, and the pay phones were unlimited talk for 25 cents, and they didn't give us the 'bum-rush' out of there - nice bathrooms, too!). At the one the was "the middle" (when you were the last car), there was a 7-11 with THE most wide-ranging soda fountain I'd ever seen...I would get the 'rainbow' in the "Double Gulp" - the 'bladder buster', the 'super tanker' - the baddest of the bad of sodas...64 ounces of love! Most I ever had in one day was 3 Double Gulps and a quart of won-ton soup.