A laptop slot 15 inches (Mine is a fairly thick pro model, and it passes without worries).
Not bad for a storage box, objectives, and all their accessories.
A separate storage location.
A bag format back to distribute the weight on my shoulders.
The ability to get out the camera without removing the backpack, always practical output.
The fastpack 350 filled perfectly all these criteria in addition to being protective enough for the gear inside. It is even possible to store a large box (with Nikon D600 Grip) + telephoto (Tamron 70-300) and its visor in the bag, and take it out by the rapid opening. Really not bad.
I managed to take 2 boxes (+ D600 and Nikon D801 Grip), a Tamron 70-300, a 50mm, a 28mm and a 100mm 2.8, a PC pro laptop (Lenovo T530) 135w its charger (Who looks a large brick), a reflector picture in its cover and some trinkets. It is not the volume that will limit you, but the weight :)
Beware though, the bag is large enough. It's been a little hiker and not very discreet. You decide if you prefer the loading capacity or discretion (the FastPack 250 may be sufficient in this case)