May I recommend this backpack, currently available:
http://www.davidclapp.co.uk/blog/vie...t-200aw-review
(This is not me, bout it is a sensible review).
I use this for serious trips when we are in the arctic or somewhere inhospitable and I am just carrying photo gear and some snacks. It is not suitable if you want to take a lot of lenses, but it will take my 5D3 and a long lens (70-200 2.8L usually) and a couple of shorter lenses. Tripod goes on fine but is best with a lightweight carbon one. It will also happy carry a Mac Air or similar in the sleeve at the back. It straps on well and is comfortable to carry - I have done an all night trek with it in the arctic to do northern lights and wild animals at the edge of a frozen lake.
It is not a frame type bag that suspends it with an air gap, but as long as it is not overloaded there is no disadvantage.
The only thing that really beats this in my experience for lugging expensive camera gear about is carbon framed mountaineering sacks, but then you are getting into serious money.