Main compartment is 16.5″ x 10″ x 4″
secondary is 15″ x 8.5″ x 2.25″
plus the 2 smaller external pouches on the front.
all the existing compartments have internal pouches to compartmentalize smaller stuff.
and not alot, but more than a few of the straps to attach any standard alice pack accessories
Bug Out pack
I has several cinch straps, for horizontal and vert compression.
has the waist strap, had the chest strap until I took it off.
The back straps can be detached at the bottom and tucked into a velcro sealed pouch on the back and the item can be carried like a vert briefcase.
I am using it primarily as my summer laptop bag, its minimilist size keeps it riding higher on my back and prevents it from resting on my rear seat on days when I ride the SV.
A while, we had also covered the 5.11 brand of packs. While pricier than the afore mentioned model, the value may be there for you. I just purchased a 5.11 brand as well, model is Rush 24. It was not cheap but is bad ass. It is very well appointed.