Re: 12 hour car trip....advice
My kids younger kids love the leap frog toys in the car - it is one of the few times dd2 is interested in practicing her letters.
We've done ispy bags or bottles in the car. Ispy bottles are easy to make - take an empty pop bottle, add small objects to spy and fill with rice. For the 15 month old leave about a 1/3 of the bottle empty so it shakes easy. Screw the lis on super tight or glue it on. We've done ABC beads in one for dd2 and animal beads for ds in bottles.
Those invisible ink activity books are always a hit because we never buy them unless heading out on a big trip.
We also have a dvd player in the car that helps a ton.