A fully loaded Keepall 55 (books, magazines, clothes, toiletries, electronics, bottled water, snacks, spare pair of shoes, etc.) can be pretty freaking heavy to carry the half mile or more to the gate. Not to mention the 30-45 minutes it's digging into your shoulder as you wait in line at security. Trust me, I know.
So I keep it light these days, pack it with about half that crap instead of stuffing it full to near bursting. Like Quiz, If I'm really going to load up for carry on, I'll use a wheeled carry on with a smaller case/larger purse perched up top.
I have two children but my days of shouldering 20+ pounds of dead weight across an airport are loooong gone.