[DonHopkins]

What kind of "CARTCHA" challenges and games might be fun to play, to prove to your car that you were paying attention to the road and traffic, yet not distract you from being ready to take over driving?

Computer vision and speech recognition could be useful for proving the driver's awake, as well as driving the car itself.

https://en.wikipedia.org/wiki/Car_numberplate_game

[1209120931]

The challenge of driving the car manually, without any hyped autopilot.

[NamTaf]

This. There's nothing else because any other task requires diverting mental focus away from the act of constantly assessing the changing environment around your car. That by definition leads to slower reaction times.