I got this idea from some parenting book a long time ago. Before a big raod trip start collecting little gifts/toys, like a small book, a necklace, a hot wheels etc. Wrap them up with lots and lots of tissue paper. Takes longer to unwrap and hide them in your car (I use the drawer under my seat in the mini-van). When the kids are sleeping, or distracted, slip one out and put it in their carseat or somewhere nearby. When they discover it exclaim, WOW! The travel fairy must have popped in and left you something. You can build your own legend, in our family the fairy wears a sparkly blue dress, only visits on trips that last more than one day, and usually only visits once a day. She's very busy you know because lots of other families are traveling too. My kids love it, maybe yours might too.