I have two Tom Bihn backpacks, a Synapse 19 and Synapse 25. They are provisioned exactly the same, with everything that I might need, all the way to advil, granola bars, and packets of tea. Of course I have thunderbolt docks in each, as well as every conceivable cable or dongle. They have built-in sleeves for my 13 inch Macbook Air. The bigger one has an extra sleeve for my work MBP 16". If I am just going up to my office, or co-working, I grab the 19. If I am travelling, or need my 16", I grab the 25. The only difference in provisions, is that I have a small usb mic in the bigger bag.
I am blessed to have bags of just the "right" size needed.