Returning to the OP's initial post, I see that he said "sat with my bag under the seat in front of me because the bins were full." I'm not trying to be horrible but, that's what that space is for.
True but, have you ever sat in an economy seat with a full size carry on trolley under the seat in front of you for three hours? You basically have to sit bolt upright with your feet on the floor immediatley in front of you - like you are in a job interview. It's not very comfy and, when you see crew getting stuff out of their bags in the overhead bins it grates a bit.
If everyone turns up with, say, a trolley bag which fits exactly in to the bag sizer at the check in desk (which does come very close to happening during school holiday season I can assure you), well there is no way all of that will fit on to the aircraft.
Why not? If every one buts their bags in "end on" in the overhard bins and the rest goes under the seats in front of them then it should all fit, no?