Originally Posted by ChinaMeng

Another way for Southwest to make more revenue could be to charge for carry-on luggage in the overhead bins. Maybe an extra $5 and your boarding pass gets denoted with a special mark. Without this mark, the FA at the gate would check your bag in. Let's say you didn't pay the extra $5; you wouldn't have to check it in at the ticket counter if your luggage was small enough. You could just go straight through security and then check it in at the gate. <color added for emphasis>