My big ones are about tiredness and sleep. I drive for work (regularly between 6-10 hour drives) and there are times where I've had to pull off the highway and lean back for a little nap. I know it's already been said a couple times though.
If you're getting tired at all, you should find a place to stop sooner than later. Like others have said, you can do some stretches or walk around, maybe even some jumping jacks or something to get the blood pumping.
I don't usually go for energy drinks or coffee, but sodas and other drinks are fine for me. And snacks do help keep you awake with the mindless energy of chewing something.
Someone said long form audio to listen to, such as audiobooks or long podcasts. Music can work, but I find it can get monotonous after a while and it'll kinda make you sleepy.