This is the same setup that I use to carry water bottles on my shoulder straps as shown in the video below. I use them on 20oz Gatorade / Powerade bottles, but they will also work on any bottle with the same size neck.
This is a great DIY project or you can pick them up here.
Included in the kit:
2 - 7" (finished length including the mitten hook) pieces of yellow zing-it with a fixed loop spliced on one end and a mitten hook spliced on the other. Each mitten hook has been modified for easier attaching by cutting a part of the clasp.
1 - 20" piece of shock cord.
To install, simply larks head the zing-it around the neck of the bottle. Then, while wearing your pack, attach the mitten hook to the "D ring" or daisy chain on your backpack.
The last step is to tie the shock cord around the bottle and your shoulder strap. Make sure you tie it so the shock cord provides a good amount of tension to prevent the bottle from "flip n & flop n" - these instructions are also covered in the video below.
All water bottle holder kits are shipped via USPS which is included in the price.
Well, because it's cool of course!