For me personally, I have to read in a car to get through the trip. Otherwise, I "feel" every slight movement of the car. Opening the window helps unless it gets too cold/hot.

Although the sound and wind can be annoying, the constant sensory pressure from the wind helps me deal with the car ride.

Music can help me, but I need it blaring to the point that I can almost feel it (not something my husband is willing to have going on) from the sound system and not just headphones/earbuds.

Reading lets me get lost in the book so that I just ignore how crappy my body feels. When we get to our destination my body will still be complaining to me, but once I start walking outside the car for a short bit I recover fairly fast.

For trips an hour or longer, expect that you will need "breaks" every 45 minutes where your son can get out of the car and walk around. Rest stops are great for this.