You've got a few hours, a car full of restless, and one (1) working aux cable. These save the day.
License Plate Game
Spot plates from different states. Keep a running list.
20 Questions
Would You Rather — silly category only
I Spy
Alphabet game
Find each letter on signs, in order. Q and Z rule out billboards.
Category chain
Ice cream flavors, superheroes, dinosaurs. Go till someone blanks.
Rhyming chain
Count the red cars
Animal sound impressions — guess the animal
Make a story, one sentence each, around the car
Odd or even license plates — call it first
"Two Truths and a Lie" — adults edition, keep it G-rated
Describe a friend — others guess who
The Alphabet Food Game
A-Z: apple, banana, carrot. Categories: movies, animals, places.
Audiobook or story podcast
Downloaded beforehand. Trust no rest stop wifi.
When all else fails: audiobook.