i find that you should definitely moderate your caffeine intake. that way you don't stop as often to take a piss and as others pointed out, you will crash very hard if you take in too much in too little time...one time i was prepping for a thirteen hour drive on 3 hours of sleep so i drank 5-6 cups of coffee and 2-3 hours into the drive i felt like absolute shit. also, if your coffee is halfway decent and you can handle it drink it BLACK; i feel the powerful flavors and aromas do more to perk me awake than the caffeine itself.
having the right playlist helps, but i find myself tuning out to my songs since i'm usually so used to listening to them, so finding a good radio station can also assist in keeping you awake and alert.
and lastly, if you're going by yourself, have some friends call you randomly during the day (and if they're good friends, night) to check up on you and chat just to break up the drudgery.