The 5 or 6 hour energy drinks are good
in moderation for those looking for a pick-me-up. If you've never taken them before, I would go with half a bottle at first to see what your tolerance is. If a half bottle gets you jittery, then they just aren't for you.
A lot of what has already been posted above is spot on. One thing that you can do to simulate the effects of these energy drinks is this: buy a dropper bottle from GNC or your local health food store of B-12 complex, and a bottle of ginko-biloba tablets. Before your tournament begins, about an hour before, take 1-2 dropper full of the B-12 and mix it with your favorite, non-carbonated drink, and two ginko pills. It will give you the same pick-me-up feeling, with increased concentration as the 5-hour energy drinks, without the stimulants such as caffeine.
Another way to make sure your energy and focus level is at a higher level is to do some sort of aerobic activity a few hours before your tournament. Nothing too strenuous, as you do not want to wear yourself out. But enough to get a good sweat going. Distress your body just a little, and make sure the activity lasts for longer than 30 minutes. The 30 minutes is key, because at approximately the 22-minute mark, (it's different for each person), your brain releases endorphins. These make you feel "good"...and the effects last through the day. If you've ever been out running and all of a sudden felt a little buzz, kinda like you're high, (not light headed, or dizzy....
OK OK...insert joke here.
), that's the endorphins kicking in. It's a hormone produced by your body, and it will give you a euphoric feeling.
I'm getting a little side tracked here, but the long-term effects throughout the day is an increased ability to focus, increased stamina, and overall well being.
Hope this helped out!