Currently I am limited to "near the car" use of additional equipment not fitting in vest or leg pocket. When I want to hike a mile or more, I carry one lens on the camera, a teleconverter in a pocket, plus the small stuff (battery, cards, socks, filter, release) in a second pocket, plus two water bottles on a belt, plus rain jacket. Bug juice and sunscreen applied before leaving the car. Tripod is a PITA to carry in its bag.
My interests are in having a good harness and frame, because those make the weight easier to carry. Also, I would like to be able to load it over the (very minimal) harness of the Cotton Carrier vest, if needed. Hydration unit, 2 liter or preferably 3 liter, is necessary.
Typical day hike load would include:
Canon 400mm f/5.6 (presuming that birding is the main activity)
Custom Brackets Basic Gimbal (a "sidekick-like" add-on to the ball head) 1.3 lb
Tripod, full size Feisol with Arca Z1sp head, total 5.5 to 6lb)
and one or more of the following, depending on shooting plan or destination:
macro gear:Canon 180mm f/3.5
landscape gear:Canon 15-85mm f/variable and nodal rail OR
Sigma 8-16mm f/variable
and of course the usual:
CPL filters, remote shutter release, S clamp or carabinier for the tripod hook, extra camera battery, extra cards, pack rain cover, own jacket, extra socks, depending on weather, extra top layer, plastic bags, lunch, maybe an additional water bottle or thermos hitched to a belt loop, probably a gardener's foam kneeling pad bungied to the outside of the pack.
That's at least 20 lb with 3 lenses, not counting the pack itself. I have an el-cheapo large pack that holds all this stuff but doesn't have adequate strap adjustment, a waist belt, or any frame. The pack is basically a (perfectly adequate) suitcase and storage unit, not meant for comfortable hiking.