Mostly I just drive without music or other stuff such as talk radio or audio books. It was different when I was younger, then I pretty much always had some music on. My friend I sometimes travel with usually has an audio book, podcast or NPR on.
I've tried the loud music thing. After a short while my brain starts shutting down from the "noise". Good for 15 minutes or so at best for me. The audio books at least keep me engaged.
Driving long distance and listening to music triggers memories of the past. I will sing to the past, On some songs I dance in my seat and sing away. Helps to get the blood flowing and release feel good endorphins.
I prefer silence. I watch the scenery, I watch out for the dangerously stupid people, and I take a break every 2 hours that includes walking around for 10 minutes or so.