So here's the problem
I put my equipment on my person in the following order - to ensure the most free movement of my camera.
1. I have a backpack with my lunch etc on my back
2. Then a small waist bag which will carrys my nikon lens, spare batteries, lens caps, and lens cloth etc which goes over my right shoulder and hangs down my left side - at waist height.
3. Finally I have my camera with my 150-600 over my left shoulder on a Peak Design strap and hanging down my right side - about hip height -
4. I then attach my monopod to my lens foot.
To access my backpack, I need to take my monopod off - put it down, take my camera off - put it down somewhere, take my waist bag off, put it down, and then finally take my backpack off.
Using a backpack to stow my 150-600 means a full stop - and a good 5 minutes to readjust and put everything on again!! Then take my shot. When walking in a group - at the moment, I pretty much decide on a lens and accept it's too hard to swap - unless we stop for lunch - and even then it's a faff!!
Perhaps I need a pair of combats to comfortably carry my small accessories - do away with my waist bag. Even still I can't see a way of gaining access to backpack when i have my Peak Design over one shoulder with my camera on the opposite hip.
As you can see my dilemma!! Perhaps I just have to accept I need an assistant to hold my 150-600 if i want to swap on the move.