I like the Think Tank belt setup:
https://www.thinktankphoto.com/pages/belt-systems
Fully configurable, great protection for your lenses. Usually I will wear my main body + lens around my neck, and maybe 2 Lens Changer pouches for extra lenses. If I want to carry a crop body with a long (70-200) lens then I will add on my Digital Holster 20. The Digital Holster 20 doubles as a small protective bag for just the body + 1 lens. The nice thing about some of the longer lens bags is that they will let you carry two shorter lenses in one medium-sized pouch. E.g. I can usually put my 17-40 and 50mm prime in one of the medium bags (designed to fit a normal zoom such as a 24-105).
Taking the weight off your back/neck and putting it on your hips is a lifesaver! I have the medium-thickness, padded "Pro" belt. The best thing about this system is that it is super flexible, so you could (for example) put a single pouch on a standard fashion belt if you're just running around town and don't want to tow a bunch of gear; and you can also use it to protect your gear inside larger, non-camera-specific bags. You can carry a body+lens and a couple of other lenses in a carry-on, backpack, or messenger bag and feel that they are well-protected.
Oh and the pouches/holsters/etc. have a unique feature that lets you "lock" them into place using the loops on the belt; or you can leave them free to slide freely around the belt. Usually I let them slide so that I can push them behind me when I am walking through bushes etc., or pull them forward when I want to change out a lens.
Oh and speaking of strapping it to your backpack: I have a backpack with little d-rings on both straps. I use Op-Tech straps on all my bodies, and they have the quick-disconnect portion of the strap, which I can then swap out with extra straps with quick-connects attached to the backpack straps. Basically, I remove the actual "neckstrap" portion of the strap, then clip the small ends of the strap (still attached to the camera body) onto the tails connected to my backpack.
It looks like Op-Tech actually makes something specifically for this purpose now:
http://optechusa.com/Videos/ReporterBackpack.html