My CamelBak Hog is on the smallish side as bags go. If I had to haul food/lunch to work it would probably be too small, although I manage food at times. So that would be my sacrifice.

I even keep my underseat bag and a folding road bike tire in it. If I affixed the bag to my seat and nixed the tire, no prob fitting lunch of some sort.

I carry a lot of stuff to work in my opinion. I am not sure about the cubic inches of my pack. It's about 3 years old and smaller than the newer ones. I never use the bladder. I keep my raingear and a pack-towel in the bladder compartment instead of the bladder.