Cheap deck bags.

I came across some Belgian patrol pack/rucksacks made of rubberized canvas that I think will make a decent deck. They aren't completely waterproof but that can be solved by using small nylon dry sacks as ditty bags. There is also a large pocket on the back of the bag. By cutting one or two pieces to fit from an old closed cell foam sleeping mat and sticking them in the pocket some floation can be added to the pack. These bags are running around $10 in local surplus stores.