I used a 1 liter soft-side Nalgene, with a strap though the cap loop and stand-up bottom, to put around one shoulder and across my torso while snowshoeing to have water near my body that would not freeze. It worked well. With a shorter strap you can lace up to two Nalgene water bottles, one in back...one in front, of appropriate size if you need extra water carrying capacity in your SUL setup, most comfortably if your pack has no hipbelt.
1. Nalgene soft-side container
2. 1" strap
3. Paper hole puncher
1. Punch holes in stand-up bottom to support a 1" strap.
2. Lace 1" strap through cap loop and bottom.
3. Put it on like a fanny pack.