Try to get enough sleep beforehand if you can plan it. You should aim for 7+ hours of sleep (or whatever is considered a full nights rest to you since some people do not need as much sleep as others) to feel fully rested. However, it is not always possible to plan ahead or get as much sleep as you want so the rest of these steps are to help you and those around you stay safe on the road.
Roll down the windows. Get some fresh air in your face to wake you up. If it's winter, the nippy air is great for waking you up and making you more alert. If it's hot outside, blast the air conditioning in your face.
Slap yourself. I'm serious! If there is no where to pull over and the drowsiness causes you to start wanting to close your eyes for just a few seconds...don't! Slap yourself in the face a couple of times to wake up!
Bring a BIG bottle of water on the trip with you. And if you can, fill it up with a bunch of ice and then top it off with water before you leave. That way you will have cold refreshing water to keep you hydrated and feeling awake.
Take a break. If you are really struggling, take a break! A lot of car accidents are caused by drowsy drivers. My doctor dad always told me that driving when really tired is just as bad as driving under the influence of alcohol. When you are very sleep deprived, your reaction times and coordination are not much better than a drunk person. Find a pit stop and take a break. Lock your doors and take a 15 minute nap if you have to. It's better to be late than to not ever make it at all from falling asleep at the wheel. Stop as much as you need to.
Bring a snack, but not a bag of chips. Avoid fatty foods that will make you feel more lethargic. Snack on some veggies or fruit and some protein. An apple and a peanut butter and jelly sandwich would work well. If you just want something to munch on, bring a bag of trail mix and some dehydrated banana slices. If your only option is getting something from a vending machine and there's no trail mix, some peanut M&Ms and Sun Chips will give you some protein and carbs to keep you going.
Anytime you are going to be driving for a while, make sure you plan ahead so you can get enough sleep and bring the proper things you will need to help you stay alert, like the ice water and snack. And maybe a pillow and blanket in case you need to pull over for a 15 minute snooze in the back seat. Just make sure it seems like a safe area and don't forget to lock your doors!
