Which camera bag? I have several. For each system (EOS, FD, Nikon, Minolta MD, M645) I include a body and a couple of lenses. After that it's pretty variable, depending on what I use the system for: extension tubes, cable release, specialty filters, assorted film, spare batteries and so on.
The main bag for each system is set up for a particular body with a couple of extra lenses and some small paraphernalia; the body is easily exchanged for another of the same system. I almost never take more than one body, unless I'm driving somewhere.
My Mamiya M645 kit resides in two bags, depending on whether I want to go 'small', or if I'm going on a driving excursion. A Billingham 225 holds the camera, three lenses, spare insert, batteries, film, etc. If I'm going out for a drive in what country we have around here I also grab a Billingham Hadley Pro, which contains a few spare backs, more inserts, extra film, and extension tubes.
After 20+ years of lugging gear around I've come to appreciate traveling light and grabbing only what's needed. I no longer take everything with me, nor do I load up on extraneous stuff like multi-tools, gaffer tape, string, wire, etc.