Before heading out on a long distance road trip make sure you get to bed early enough and get enough sleep the night before the road trip.
This will ensure you're well rested so you won't be as tired on the long distance road trip and if you have to you should take a sleeping pill the night before to make sure you get enough sleep.
For some reason whenever I know I'm heading out on a long road trip the next day I can't sleep easy the night before so I always take a sleeping pill 30 minutes before bed and I make sure I have everything packed in the vehicle and camper the night before if I'm taking a camper with me.
Then I get into bed and drift off too sleep and get a good nights sleep.
During the long road trip I drink coffee to keep me alert and awake and I take frequent breaks ever 1 hour and pull off for 20 to 30 minutes to walk around which helps me stay awake.
You can also play some music which helps some people stay awake and avoid using the heater if possible or don't turn the heater on too high because that can make some people sleepy.
If you're feeling sleepy you should pull off the road and take a break and take a nap even in a parking lot such as Walmart or a gas station parking lot.
Take a quick nap even for 30 minutes which can help keep you refreshed.
Eat a good healthy breakfast before heading out on the road trip and eat some healthy snacks while you're driving which keeps your energy levels up.
If you can have someone else take over driving for awhile if you're getting tired and try to sleep while the other person drives.
Then switch over again and let the other person sleep while you drive.
Some over the road truckers do this in some places.