Sunflower Seeds... the un-shelled ones that you crack in your mouth, fish the seed out and spit the hull into a cup.
Believe it... works amazingly well. I discovered this on a church ski trip to New Mexico. I was driving the luggage truck (i.e. pulling a cargo trailer with the groups luggage) and the youth director was with me. He was supposed to spell me off but unbeknownst to me he has some fairly severe sleep apnea and spent the entire trip passed out in the passenger seat. I like to drive so I didn't really mind until around about 03:00 the next morning (yes, we drove straight through) when I started having extreme difficulty staying awake. I tried gum, coffee, candy etc etc. with no luck. I had brought some sunflower seeds because by kids like them and I thought I'd see what all the fuss was about. Well, I popped some in my mouth and started cracking and spitting... after awhile I realized I was wide awake but I didn't put 2 + 2 together right away.
One of the things about sunflower seeds is that when you first start, your tongue and lips get a little sore after an hour or two so I quit... and withing 3 or 4 minutes was starting to nod off again... so I thought I'd go back to what had been working, sore tongue/lips or not. Guess what? Loe and behold I was wide awake again. When we finally got to the resort by mouth felt like it had been through the grinder, but I wasn't a red smear on the highway somewhere.
Since then, I've always made a point to have SF seeds on any long trips and have told all my friends, family and acquaintances about them. Every one that has tried them has confirmed their efficacy, including a friend who drove straight through to Florida for an Aikido clinic and then straight through on the return trip. He told me he doesn't think he could have done it without them.
So, try 'em out. If just one of you is better able to stay awake and avoids dying due to sleeping while driving, I'll consider it my good deed for the decade!
One other thing that is very nice about this trick... unlike coffee, you can go to sleep within minutes of quitting and you don't have to stop for bio-breaks every 30 miles/minutes.