Mark: The fish bags don't seal either. Their saving grace is how small they fold down -- for inclusion in an Altoids-sized PSK. A bigger bag, especially with handles, might be handier in actual use. You'd have to put the fish bag in a sock or other plastic bag or find some way to help it stand up.

I've just received some Platypus 1L plastic bag bottles and carriers for use when backpacking. (I set up base camp with a 3L bladder in my backpack, but like to go exploring with just my jump bag and some water.)

http://www.cascadedesigns.com/platypus/bottles_carriers.asp

One is just a net bag with a strap and that seems really promising for either my hiking application, or for inclusion in a larger PSK.