When my wife hikes she carries a DSLR. We figured out that for $15-$20 she could get a small soft padded case and then we used a web strap to go behind the two backpack shoulder straps (down low) and then in front of her waist and through the back of the case to form something of a fanny pack. (You could just go around your waist, but I'm recalling that the webbing we had was too short.) This gave her instant access to the camera and without too much rigging she never complained about it. She has two lenses. One on the camera and the other fit snugly in the case.

I have the case right here... Quantaray case - black with purple trim... 10.7 oz. (i can't find a picture online)
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I always forget and make it more complicated than it needs to be...it's just walking.