Rule #?? (No idea actually, it will have to be worked in.)
Seats and bags: When flying within the USA, in coach, if you have a rolling carry on, choose a seat in a row in the middle of the section.
See, if they load starting in the back (say row 26) and you are in the front, say row 7, on a near full flight, by the time your row is called, they may be checking the carry-ons because the overhead compartments are full. If you are in, say… row 15, you should be okay.
I have just about given up the rolling bag for this and other reasons.
So, if you just have a smallish backpack, you can join me up front since you and I will not have to worry about losing our bags to the seemingly shrinking overhead compartments.