I recently got a soft shutter release for my new 100F, and it's awesome, definitely worth the £3 or whatever. A brass one looks like the dog's danglies on a silver 100F too.
I've also got a thumb rest that slots into the hot shoe. It makes it ten times easier to use one handed, but it can catch on your clothing when it's hanging on a neck strap.
Oh and get a screen protector too!
edit: I 3d printed my thumb rest and it's a bit higher than the ones on ebay etc, so maybe a lower one would interfere with dials like David says.
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