After much trial and plenty of errors, I now keep all I use on the G9 in one bag, then I have smaller bags for the others with what usually gets used on each of them, then a bag for flashes, slave triggers, ball mounts, cables etc, and finally another bag with bits that could get used on any camera, but not often.
I also have a couple of small bags that will just carry a camera and lens as the majority of times, that is all I will use for that day.
I now hardly ever have to change things around, except for example to "borrow" a lens from the G9 bag to use on the G80, but at least now I know exactly where everything is, and the bags are not so full things could fall out getting to something else.