Depending on the size of the camera bag, the L.L. Bean Quickload Travel Pack has a fairly large outer pocket (not the one with the mesh organizer) that can easily be accessed without undoing the external straps. I have put a large Tom Bihn Cafe Bag in it (13 x 12 x 3) with the idea that it could be easily removed should the main bag have to be gate checked.
Fortunately, I never have had to. It always passed muster.