Letters On The Go- great car trip activity. Could use ANYTHING on the plates- colors, shapes, letters, environmental print, etc. You could also have a "checklist" kind of plate with items like "vanity plate", road signs, certain color cars, rest stops, etc. like a travel bingo. For multiple kids make it a contest, older kids or more hands-on kids, give them a bag and have them tear off the tab and put it in the bag. Upon arrival at your destination, the one with the most tabs in the bag wins.