Revelate Designs is at the forefront of on-the-bike bag design a perfect example is the Mountain Feedbag that mounts on your bike's stem with a multi-strap system that eliminates sway and is great for carrying anything you need close at hand.
One-handed opening and closure with no fumbling to grab cord locks
Three external pockets for gels and trash
Three-layer construction: outer fabric, foam (for insulation and stiffness) and liner
Mounts to either side of stem with adjustable attacment points
Fits bike water bottles, Nalgene bottles, or bear spray cans