Coffee is the most glorious beverage known to humankind. It comes from beans (most likely of the magic variety) and makes you hyper. Drinking too much may cause lack of sleep and crashing the next day, similar to the effects of milk.
Use During NaNoEdit
During NaNoWriMo, coffee is the drink of choice for many sleep deprived writers, though some (such as zxicefirexz) might preffer such beverages as tea. It's perceived waking-up effects make it very useful for those who have little time for sleep during the frantic writing of November. Coffee is also a very useful drink for All-Nighters, or staying up all night to write.
There are many kinds of coffee. The best type for NaNoWriMo in most cases is Robusta with very little milk or water - the less diluted and more caffinated it is, the better. Or a frape.