I have been wanting a fly fishing bag for a while and mulled over it all winter. This is what I finally came up with. It is a USGI combat lifesaver bag. I really like the way it folds out into three compartments. Will be trying it out in a couple of weeks. Tell me what you all think.

I have a couple of those in the basement, have used them as first aid kits for many years. I think it would work very well as a fly bag, especially for keeping all of the little things together. I tend to use rather large flies on my trips so my fly box would not fit into that bag, but I always struggle with keeping all of the little stuff together (i.e. extra leaders, tippets, etc.)

I think you have found a winner!