I was up to 3 or 4 large Tim Horton's double-doubles per day when I flew medevacs. It was the only way to make sure I could keep my eyes open at any time of the day (or night). The downside to that was I spent $15/day on coffee and cookies (it wouldn't be right to get a coffee without one of the caramel/chocolate/pecan cookies that Tim Hortons offers), and I had frequent stomach cramps.
Then one day I tried Red Bull. It was great - it tasted like liquid candy and it went well with vodka. And at 630am the following morning as I sat, tipsy and wired, in my hotel room, I realized that it had lots and lots of caffeine.
At $3 per can we could have no long term future, and I have settled on its cousin, Red Rain as my fav energy drink. They are only $1.25 per can and have as much caffeine as 2 cups of coffee, but without the stomach rot.
They also work really fast - if I wake up from my afternoon nap and feel like a clubbed baby seal, I just chug a Red Rain and by the time the contents are in my gullet, the fog has lifted.
What's your secret for staying alert in the cockpit?