I'm another member of the ranks who've got an unused monopod sat in the corner. I'm sure I'll use it one day, maybe.
I've also got yellow and orange Bay-1 filters for my Yashmat 124 but I've only ever shot colour film or slides through it so they've never been used.
Nikon F100, bought thinking that it's one of the ultimate film cameras, used once because the amount of automation moves my involvement in the process a step or two back and it feels like I'm shooting digital without the option to chimp. Same goes for the lenses I have for it.
Zorki-4, classic rangefinder looks, has sat on a shelf for the last couple of years because it's too bulky to slip into a bag like the Electro 35 GX, which also doesn't get enough use.
I'd better stop, I could go on like this for a while...