The original bailout bottle system is still going strong, proof that a good idea never goes out of style. The Spare Air 300 unit holds 3 cubic feet of air and comes in a fluorescent yellow nylon carry holster that mounts almost anywhere. With a Spare Air your emergency air supply is always on--just clear, breathe and go. Each unit comes with a fill adapter that lets you transfer air directly from your main tank in seconds for easy filling. $299 (nitrox model, $320). www.spareair.com.