I have a similar kit. Many forums have gone on for months over what can be included and that plain and simple depends on your climate and area. But the best idea I have heard, and I wish I could claim it, was to use a Nalgene water bottle for your kit. A carabiner on the loop that holds the lid on and it can be attached anywhere. Light and waterproof with a bottle to treat water in. If you are near a Gander Mountain they started selling these as, Hunter in a Bottle, Survival in a bottle and Fisherman in a bottle....each with a little variation fo items in it.
I sent my GPS with a friend as he canoed the boundry waters and dropped the GPS in a wide mouth water bottle. I added a Carabiner to the loop that holds the lid. He used it the whole time. Waterproof, still could see the sky, room for lots of spare batteries, protected from bounces and enough air that it would float if it became unattached. Each of the kids were supposed to have made a Personal Survival Kit (PSK) to carry as they did 80+ miles in 6 days.
Gadget54