* Drink caffeine -- Everybody's first choice, but I probably drink less on the road than when at home. Too much and you get jittery, nauseous, and need to stop too frequently
* Drink fluids - You definitely need to avoid dehydration. I drink Gatorade, water and orange juice
* Eat salt - It's not healthy, but salty foods are best for staying alert
* Just eat -- Eating keeps you busy, best are those foods you can easily measure and parse out, like gummy bears, sunflower seeds, or mints: Okay, five more miles and I get a gummy bear. Sunflower seeds are great because they require work.
* Talk -- To anyone, or anything
* Sing -- Not when your co-driver sleeps! But this is by far the most effective way to stay awake
* Do leg lifts or hand squeezes -- Basically, any physically activity requiring effort. I'll hold my left foot off the floor as long as possible, a friend like to bring one of those muscle-man grip squeeze thingies.
* Shake -- As vigorously as possible, shake your head or your arm or anything to get the blood flowing
* Rest one eye at a time -- I don't do this, and can't recommend it, but I know of a driver who will close one eye at a time!
* STOP -- No schedule is worth endangering yourself, your co-driver, your equipment, or the lives of others on the road. Stop and take a break, or walk around, or take a nap.
* Listen to talk radio -- The more controversial or "stupid" the better, because your arguments keep you alert.

Ultimately, if you work well with your co-driver, you shouldn't have a problem staying awake. If you split the day in two, you're "on" for 12 hours, and "off" for 12 hours. You can sleep ten hours out of that! In some ways, I get more rest than when I'm at home...when I'm often "on" for more than 12 hours.