<p>A changing bag indeed. If you use film regularly, it's the best investment after your camera. To make it really useful, get a large one for emergencies like you have now for loading tanks for home development. The larger the better. It can get quite clammy when loading several reels. And also get a small one for travel. When in Amsterdam some years ago, I stripped the perforations at the last frame putting me in much the same situation you are in. Went into a photography shop just before closing time and asked if they could help. Same answer as you got. But when asked if they had a changing bag someone lit up and brought it out of a shelf. None of them knew how to use it. 3 minutes later I had the film back in the cassette, all smiles. Now my smallest changing bag always comes travelling. It's a life saver.</p>