In my personal experience, drinking coffee can be an enormous boon to productivity. See FortuneCookies for some humorous testaments to this.
If you've never drunk coffee, but want to try, I must warn you that it's addictive. However, it's not as addictive as a lot of drugs, and even addicts find it harmless enough that they serve it by the tens of gallons at Alcoholics Anonymous meetings, Narcotics Anonymous, and so on.
The Caffeine Advantage is a superb book that explains dosages and the "paradoxical" effects of caffeine. The "Coffee Achievers" commercials from 1984 tried to promote coffee as both a stimulant and a "calm moment". It seems silly, but it has a basis in science, as The Caffeine Advantage explains. (It has to do with the Yerkes-Dodson Curve.)
I recommend coffee rather than cola or caffeine tabs. Tea makes a nice substitute on occasion, but does not help with productivity as much. Both coffee and tea contain chemicals other than caffeine. Tea has more of a "cheerful" feel; coffee has more of a "go get 'em" feel. Some people think this explains much of the difference between British and U.S. national temperaments.
If you don't like coffee, I recommend starting out with some nice flavored drinks from Starbucks. Caramel macchiato tastes great. Be sure to drink your coffee while it's hot; it tastes like crap if you let it get lukewarm. Strangely enough, good iced coffee tastes pretty good. All my opinion, of course. Mindhacker contains a hack about how to acquire a taste.
Of course, nothing will ever make you superhumanly productive, 100% of the time. But coffee probably will boost your productivity significantly. A great mathematician, Paul Erdos, once said, "A mathematician is a machine for turning coffee into theorems." He typically worked 19-hour days.
A recent article made a defense of coffee with respect to its health benefits: The Case for Drinking as Much Coffee as You Like.