http://americaonwheels.org/AOW%20Car%20Games.htm has several, most of them I've never heard of.
I have used the 'farthest state plate' to keep my mind active and looking around, and when on a long drive with someone else the name game is a fun and competitive way to see who can start the next name with the last letter of the previous full name. ie Jack PalancE to Emilio EsteveS to Steven SpielberG to George Burns. This was a great way to waste a lot of time on watch while I was in the Navy too. It gets competitive when someone has to start a name with a X, Y, or V. Yasmine Bleeth was always a good bet.
Name foreign cars from a certain country was a good one too.
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