kyl3688631 wrote an answer about CamelBak Charm Hydration Pack - Women's on June 29, 2011
For me the pack fits fairly snugly without a chest strap, but I rigged one for my long runs when I have the reservoir completely full. This will only work if you have enough tail from your shoulder loops for the ends to meet together when you hold them across your chest. I took a small carabiner and clipped it through the loop at the end of one of the shoulder straps. Then I approximated how snug I wanted the strap to fit across the chest and tied a knot in the other strap so that when I clipped the carabiner into the other loop, the strap was snug across my chest. It took a little trial and error, but it seems to work pretty well and it keeps the excess shoulder strap from swinging around when I run.