First, I use a harness, but most jacket BCs have places that this can work with.
Anything that I need and don't want to loose is put on a leash that has a bolt snap at one end and is either run through the build in loop on the object or has a shackle on it. I also never use a knot on the leash, I learned a long time ago how to do an eye splice with nylon rope.
Not for a camera, the leash is long enough for me to hold the camera in front of me and have it cliped into my upper left harness D-ring. I have the camera in my left hand most of the time when I am not shooting. But if I have to have both hands free, I do a little toss out and towards the back with the camera and it will stay out of the way next to my tanks. If I am running a stage tank, I may have to guide it back but it is easy to do once you get the hang of it.
When entering the water I will either have the camera handed to me, or I will clip the leash off to a line from the boat, drop it over the side, and get it after I roll in. Getting out is the same way, clip it off or hand it up.