carrying photographic gear poses health issues with substantial risk of neck and back issues when carried for long periods
unless you really need a heavy system, think carefully about buying a lighter more compact system such as Micro Four Thirds system - your body will thank you for it in both the short term and long term
the two obvious solutions are:
shoulder straps such as those which come with your camera
there are many problems with shoulder straps including:
takes a little time to put the strap on the camera and take off
dangerous for your camera when camera is on a bench - someone walking by can easily catch the strap and your camera ends up broken on the floor
gets tangled up in your backpack, especially if you have two cameras
your camera is exposed to damage when bushwalking or climbing rocks unless you use one hand to stop it swinging freely and hiting ricks, but then you lose that hand for stopping you falling
the rear EVF of your camera tends to point up at the sun exposing it to potential permanent sun damage
will cause problems with your neck and back
the camera strap lugs on some cameras can be a weak point and result in the lug pulling out
the main problem with carrying it in your backpack, is you will miss many shots as you have to take off your back pack to access your camera
alternate solutions
belt mounts
there are various options
take care choosing the belt buckle as some cheaper ones may accidentally un-buckle!
ThinkPad belt system
one of the best belt solutions which also allows good protection for your camera
best used with camera/lens weighing < 1.5kg in each pouch otherwise the weight tends to twist the belt outwards with loss of support over the pelvic brim
for heavy pro cameras > 2lb, you will need to get the heavy weight solution such as:
Spider Camera Holster SpiderPro Single Camera System at $US135
Chinese full metal mount versions with hip pad on Ebay (~$36)
Spider Camera Holster SpiderPro Dual Camera System at $US235
less camera bounce and swinging and perhaps safer for your camera than the Chinese versions of the Black Widow holster which have a metal ball which can unscrew unexpectedly and drop your camera
Spider Camera Holster Black Widow Holster $US49, or the Chinese made equivalents on Ebay (~$8-15), or Chinese made full metal versions ($23)
consider adding a Spider Camera Holster Black Widow Thin Plate ($US16) if you also wish to have a tripod mount plate sitting on your camera - this should also work with the Chinese versions
consider adding a protective pad for your hip:
Spider Camera Holster Black Widow Belt Pad ($US16)
Capture Clip Pro (~$US80)
best for smaller, lighter cameras as excessive torque issue with heavier cameras
changing a lens is easier since the body is locked into a fixed position when engaged in the clip
not great for when using flash, etc
this seems to mount the camera with EVF towards the sun which is problematic
these can be combined with waist belts designed to attach other items such as lens pouches and even small tripods
shoulder harnesses for 1 or 2 cameras
usual hanging designs
generally have similar issues to shoulder straps and may save some neck issues
secured designs
Camera Vest for All Camera Types made by Cotton Carrier is a unique chest harness system $US149 or $US189 for additional waist belt harness for 2nd camera