And by that, I especially mean, formats / cameras that you have everything you need to shoot, but don't.

For instance, I rarely use my 2x3 press camera. I have the film, the holders, and everything else I could need... But I don't use it because 2x3 sheet film is so irritating to work with... There's no good way to process it...

Don't even try to mention trays either... That's not a good way to process anything... hah.