The Janus Extension Pocket by Maxpedition is an excellent add-on component to attach to other Maxpedition gear, with or without the extension, to increase storage capacity and versatility. I use the Janus by attaching it to my 2" shoulder strap on my Maxpedition 12-Inch X 5-Inch Bottle Holder. The extension strap can also be completely removed which is what I have done since I am not using it as an extension. Inside the Janus is a small first aid kit that I use when on short hikes which includes an assortment of Band-Aids, 5x9 surgical dressing, Moleskin for blisters, anti-bacterial ointment, alcohol preps, Advil, Aspirin, Imodium A-D, Benadryl, tweezers, anti-bacterial hand wipes and a magnifying glass. For those who would not be using it as a first aid kit the Janus will easily hold items such as a cell phone, wallet, keys, small pad and pen, lighter, compass, emergency space blanket, whistle, emergency signal mirror, etc.
The Janus features are: 8" x 4" x 1.5" with internal dividers, elastic loops and durable dual zipper opening. I have never encountered a zipper failure on any Maxpedition product. It weighs 8.4 ounces has PALS webbing for attachment using Maxpedition 5-Inch TacTile - Pack Of 4. The Janus is water and abrasion resistant and extremely durable. It will handle any abuse that you can dish out.
If you need an extension, extra storage space and versatility then I highly recommend the Janus by Maxpedition.