At the moment, I'm carrying my 5D2, 70-200 f/2.8 II, 35L, 24L, Macbook Air, + filters and accessories inside a Thinktank shoulderbag.. It is pure torture for my shoulders, and I don't think it is good for my physical health.Now I do not know your needs but is that Macbook really necessary to carry with you? I mean do you edit your photos before returning to home?
Also if you shoot landscapes (and not portraits) a 70-200 f/4L IS would be a joy to use and carry (speaking of personal experience since I have both)
If you are a landscape shooter I believe the above 2 changes will alleviate your burden.