[nostrademons]

Also stand-by passengers and people who catch an earlier flight. It used to be that at least one airline (United?) would let you switch planes for free if you asked the gate attendant <10 minutes before door closing and they still had room, so you'd often end up with a few savvy travelers loitering around until the very end of boarding. This hasn't worked the last couple times I tried it - they charge a fee - but I still almost always ask and see what the options are if I get to the airport a couple hours before my scheduled flight and have only carry-on baggage. Once I even managed to switch a 1-stop to an earlier direct flight: I paid the $50 fee but it still ended up cheaper than buying the direct ticket up-front.