Interesting thread. What counts as an accessory and what isn't? Is a strap an accessory? A lens hood? How about an 'accessory' finder for that 21mm lens? I put a piece of tape on the base-plate of my cameras, on which I write the film type, EI, and other brief shooting notes; when I finish a roll, this gets wrapped around the cassette for later reference. Does that count as an accessory? I went through a phase of trying out lots of bits and bobs various people have developed for M cameras- softies, cases, add-on rewind cranks, winders, Lutz's Sling, grips, and others. Some I still use, some I don't. I keep a soft release on or near all my M's, because (even though I have come to dislike most "accessories") I find that for me they really do work. When I want to put an M on a tripod, I use a grip, to get the centered mounting hole- and sometimes I use a grip with larger, heavier lenses. I keep a Sling on my Bessa L (I find the camera too light for a neck strap but, the Sling is perfect with it).
I like the Rapidwinder, and I might still have one if I still had a camera with a motor lug- but I prefer to shoot with M3's, and have sold off all my later M's. When I find a deal on an M2, I might try to find an M2 version- but (Tom, are you listening?) if you made one that would work on the M3, I'd be sorely tempted...I know, I know, it's a tall order...
I use neck straps, lens hoods, finders for lenses my cameras don't have frame lines for, LTM adapters, meters, filters and flash units. Roger brings up the valid question of whether these are accessories or not, but anyway, for me, these items add necessary functions. I suppose any accessory can add features or functions that their users see value in, so I wouldn't regard others using them as pointless or silly, even if I wouldn't use something myself. There is plenty of stuff I picked up along the way that I now regard as, let's say, superfluous. I'm all about function, and for me, less is more; these days I try to use as little gear and extra stuff as possible to do what I want to.
Anyone want to buy a cheap leather half case?