A particular type of coffee available in sunny ol' England, which has(through methods unknown) been 'enhanced' using guarana, an (according to the packaging) 'herb used for centuries by the amazonian indians as a powerful stimulant'

Basically, this stuff comes in measly 100g plastic pots because it's so unbelievably strong. I had two heaped teaspoonfuls in a mug of hot chocolate - because quite frankly, it doesn't taste very nice WITHOUT the hot chocolate - and it's kept me awake for the last 10 hours without any hint of sleep creeping up on me, even through the alcohol-induced haze. In fact, when I downed the entire cup in one go, my body started overheating - my face getting extremely flushed and my lips reddening to the point where it looked like I was wearing lipstick(I wasn't).

This powdered form that I probably shouldn't have consumed earlier on apparently contains 1.75% guarana extract. It's not explained what exactly is extracted from the guarana; but judging from the general purpose of this beverage I'd say it definitely includes the caffeine content.

The same brand also comes in a sort of self-heating espresso shot, however, which I've only managed to find in tesco's so far. This neat little package consists of basically a plastic tube with some relatively thick cardboard packaging wrapped around it - the plastic tube is essentially a container filled with a couple of chemicals(No idea which at the moment), which react exothermically when mixed to heat the entire container up. Another container inside the one holding the two reactive chemicals contains some cold, ready made espresso.
All you have to do is press the convex button in the bottom of the outer container inwards so it becomes concave, thus releasing one of the chemicals - shaking it then mixes the two and heats up the espresso shot inside, giving you an instant, piping hot espresso boost. I can't say it had quite the same effect on me as the ordinary powdered form did, though - probably because there's less there.

Offical website: http://www.rocketfuel.uk.com

Update: It looks like they're now selling Rocket Fuel tea. Apparently it's the same principle - just standard tea(In tea bags) but with added guarana. It tastes pretty good, imho, and definately has more of a caffeine kick than the regular tea I drink. What more can be said?