I had a shoulder bag 'made to measure' almost, a few years back, takes a detachable collapsible (washable) hemp bucket and a compartment made for my flask, and another for scales or camera. Totally brill! I can't find the contact number though, although the guy who made it wasnt Trev or Tony (sounds like I know 'em both) although I am sure it came from an ad in coarse fisherman or similar.
Try googling it and look back as far as you can!