I am intrigued at the extent to which this thread has focused on the tactical type of day pack, which in my experience, aren't all that great. I bought a Maxpedition Vulture 2 a few years ago,drawn by its sturdy construction and adaptability (all those molle patches). Can't say I am too impressed, however. It is clunky and rather heavy, burdened with a bunch of features which only add to the weight, like load lifter straps which can't perform as such, but which look dreadfully cool. Its capacity is rather small,at 2800 cu. in.
PALs Molle kit can be heavy and not very space efficient, but it is very flexible and modular. I think that these Heavier packs can be useful for folks especially in the USA so as to keep kit and things adequately organised. i.e. different pouch/zipped compartments can be used for various uses such medical kits, shelter kits, cooking and stove kits etc. (Although for some reason rarely a sleep system kit

) The weight is a secondary after thought as walking carrying heavier load outs will be secondary to just slinging them in the back of a vehicle.
There is quite an influence on users of these military inspired back packs, whether they are cheaper Chinese made knockoffs or some rather overpriced backpacks such as Maxpedition Vulture 2, probably due to the numbers of Youtube BOB videos out there. Most of the back systems on the Military influenced backpacks do fall quite short compared to the likes of a good Lowe Alpine adjustable back system and full hip belts to load transfer to the hips etc. They are backpacks not Bergens. These military back packs should really be used with appropriate webbing systems such as a Molle battle belt harness to better distribute the loads being carried etc.
Most of these folks, who produce these BOB videos are also well armed so press ganging a few civilian Sherpas into action to carry their uncomfortable and inadequate 60+lb packs during SHTF really shouldn't be a problem..