True. Going by the guys profile of Pt.91, his job probably entails showing up at the hangar/FBO, putting his stuff away, getting the plane ready, then greeting the peeps he's gonna fly that day. Then reverse the process at the end of the day/trip. Having little, if ANY time in airports commercial positioning in uniform whilst wearing a backpack.

As opposed to all the (insert Legacy/LCC/Cargo/Regional/Fractional pilots here) we've ALL seen at one time or another.

To the OP, I don't take a backpack, or any other form of man purse to work as I'm able to get all my crap in my roller.

But when I mountain bike/hike, I have an Opsrey brand top loader 33 litre daypack that has served me well. Has the water bladder slot, as well as external water bottle holders. It's proven to be a very tough/reliable piece of equipment and the "airscape" style spacing they design into the pack helps keep perspiration between my back and the pack to a minimum level.

I know they make a variety of sizes and styles that could be what your looking for, in more conservative/professional colors (black/dark gray, etc) that won't look out of place attached to a roller.