Keep a set of batteries in your pocket to keep them warm in case the set in the camera go down. I've heard of people using pocket warmers inside of their camera bag (not right next to the film or directly touching the camera bodies) - but I haven't tried it - seems the lenses would fog up as soon as you took them out. I usually worry more about keeping myself warm more so than my equipment. Get a pair of gloves that you don't mind cutting the tips of the fingers off, then get a pair of wool socks and cut about 5 or 6 inches off the toe. Sew the toe sections to the glove at about the knuckle with the open end of the toe facing the tips of the fingers. That way, you can flip the sock portion over your fingers to keep them warm, and flip it back off when you need to adjust camera settings. then again....Key West sounds pretty good....?