I tend to be a fanatic when it comes to backpacking and camera gear. There's NO WAY I'm going into a pristine, alpine location on what may be a once in a lifetime visit, without carrying the necessary equipment to thoroughly capture the vistas with the highest quality. I want NO REGRETS once I return home. That mentality does come at a physical price as my personal pack is always right at #60 for a week long trip. That usually translates into #40 for pack and hiking equipment/supplies and #20 of photo gear which includes my 7D, 24-105, 10-22, Sigma 50-500, Gitzo mountaineer carbon fiber tripod and a variety of filters, cards, remotes and filters.
I have found the Lowepro zoom AW chest packs to be the best for such an approach. I can keep my camera with 50-500 on my chest for quick access, I can keep quite a quantity of the other gear in the same pack, I can wear it around my neck, or using the previously mentioned straps, I can attach it to the packframe for less weight on my neck. This also provides a completely waterproof option as the AW series packs have a built in rain hood.
Many won't carry such a load, but the images I have brought home with me as a result of carrying top quality gear more then make up for the physical discomfort, and I'll continue doing such until I am physically unable.
I'd still carry the 5D III and as much lens as physically possible, especially if you are planning to use the images for anything more then viewing.
As Cotton Carier owner, I'd recommend the Toploader AW packs above the CC for the protection and also the extra room for other equipment.