This is when the PSK comes in to play. I always carry a 1 gallon Zip Lock baggie in my PSK. The last 2 times I used one was to store pistol magazines as I was crossing a stream, and the last time was used as an "ice pack" to a friends sprained ankle.
Zip Lock baggies can be rolled down very thightly, and banded with a little duct tape ( that comes handy every so often ). they are as useful as 550 paracord. Great to have around.
P.S. PSK ( personal survival kit ). Check out Doug Ritter's survival packs.