Just for the sake of cataloguing, I made a mind map of a comprehensive small-format camera system. Components in black are things I already have. Those in blue are things that I either eventually want more of, or eventually want better versions of. Things in red, I don’t have at all. Some of the items listed are general (‘lens hoods’) while others are specific, like a particular studio flash unit. Almost certainly, I have overlooked some things.
Clearly, there is a lot of expensive stuff you can use in combination with an SLR or dSLR body, and this listing doesn’t even include chemical or digital darkroom supplies. For those who aren’t wealthy, assembling a good fraction of this stuff is a multi-decadal project.
See also: Lens selection survey