Adventure Racing for Geeks

Bike... front vs full suspension... 27" vs 29"... check out cyclocross and what they recommend... you'll likely end up doing some road riding so I would keep your tires inflated well. Take a spare tube.

Most hackers I know either drink a ton of caffeine or a ton of water (damn healthy bastards). These keep your mind energized! In fact there are only three things that I consistently rely on to energize me when I'm coding: strong coffee, loud music in wireless can headphones, and a really bad urge to pee.

Anyway, these same liquids work for energizing your body! In fact, for me anyway, both are required in large quantities. The one element of essential adventure racing gear beyond your mountain bike is called a camelbak. That name, as well as the look, are pretty dorky, but this thing has real tangible benefits to get you through 10 hours or more of racing. You definitely want to put at least some water in there, but I spike it with an energy drink or two. My brand of choice is Sobe life waters, they've got guarana and other caffeine sources depending on the flavor but not enough to kill you and they taste great.