That is COLD!!!! Make sure you dress well. Warm gloves, wool socks, maybe chemical hand/feet warmers.

Other than the temps, it will be lots of fun. My teammates and I do a lot of gravel trail riding in the winter (pea gravel) on our cross bikes. It is much safer than the road when temps drop below freezing, and is just nice for a change of scenery. However, I am a temp wimp, and when it gets as gold as 15F, I bust out the trainer . . .

I think you were kidding, but I still wouldn't put coffee in the camelbak!! However, assuming you are driving to the ride start, keep a thermos of coffee or something warm in the car, and a change of clothes. If you get wet out there, and you probably will (sweat and/or water on the trails) you will want warm, dry clothes immediately.