I would highly recommend something to carry fluids, but my preference is a hand-held bottle (12 to 20 ounces). Having just done a high altitude mountain bike race with a camel back, it would advise against it. Pushing your body to the max, trying to breathe as you approach 14,000' and having to suck out your liquids through a long straw really sucks. It's WAY more effort than squeezing the liquids into your mouth.
