Never pay to check a bag when flying.
If you print your boarding pass before getting to the airport, you can proceed straight to security. TSA doesn't care how many/what size bags you have, so you'll be able to carry your luggage through with you. The airline will then gladly offer to check your bag for you free of charge at the gate (especially on a full flight.)
That works if you don't pack anything that isn't allowed on the plane, such as liquids or potential weapons (apparently many thing I travel with are potential weapons). Or if you aren't flying Spirit.
When I used to fly Spirit relatively often, I'd always bring a backpack of any size, with no issues, and without paying. But a rolling suitcase of nearly any size attracted their attention, and the fee to check such a bag last-minute is much higher than ahead of time, so I witnessed many a verbal altercation between Spirit customers and staff over gate-checking bags. One reason of many I try to avoid that airline whenever possible, but $9 tickets to Vegas were just so hard to pass up during the Before Times...
