Let's be up front about it, compared to "real" photographers, my equipment ain't for shit. The Nikon D5600 is less than $600 and the Nikon 200-500mm lens is less than $1,300. Both less if you shop around for good used deals. The lens is marvelous - heavy, clumsy, with some optic limitations, but simply marvelous for the price. Yes, I envy my mentor, Brian Plath, who buys and sells cameras and lens like ... well, he does it lot. But frankly it shows in his photos. He continually humbles me. This posting is a lot for him, because he has helped with advice and he appreciates a good Rube Goldberg hack.
Arthritis? Simply age? Whatever, I hate weight on my neck. This is my field set up - camera and binoculars (or a second smaller butterfly/birds-in-bushes camera) both hung off a diagonal strap on my off-hand (left) shoulder.
Aside: My "smaller" camera is a Nikon D5500, same layout as the D5600, with a Nikon 18-300mm lens. If I had to have a single lens it would probably be the 18-300mm.
The strap also has a lens brush, and an extra battery and SIM card.
The lens has a removaable ring for mounting to a tripod, but if I mount that to the strap the camera/lens hangs awkward and bangs my hip. So I have a couple of layers of fabric tape at the center of gravity and (now it gets extremely technical) a D-ring and a hose clamp. The metal ring replaces a couple of zip-ties, and for a while a piece of wire I picked up off the street.
As my late father said, "It only cost a few pennies more to go first class".