Engineered Garments lets you keep that thang on you with their ever-versatile shoulder vest. Existing in a sort of accessory purgatory—stuck somewhere between bag and outerwear— the Shoulder Vest can slip under a coat or be rocked over-the-top for the especially bold types.
The asymmetrical design means that it's going over your left shoulder only, which makes sense because that's usually where you'll get a pocket on a shirt if there's only one.