Camera goes in a holster mounted on the shoulder harness with a couple of carabiners.

http://www.thinktankphoto.com/categories/holster-camera-bags.aspx

Extra stuff goes inside the pack in one of these:

http://www.adorama.com/MSKITCUBEBK.html

The Kit Cube is large enough to hold a 70-200mm lens (hood reversed), and a large flash unit and another lens. I use it in my day pack -- great design.
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--Ken B