If you're booked on the first flight of the day and you're not sure if you'll get on a later one, your options are slim. You can either wait it out with everyone else - or you can do the smart guy thing and book a day pass upgrade with access to airport lounges from your airline.
All of the big-4 US airlines offer day passes to their lounges for $50. You can usually get your hands on one through your airline's app. And there are a few reasons you will want to do this and do it quickly. For a start, you're likely to get to the most efficient ticketing agents in the lounge area - that's handy if it's crucial that you get on any available flights that day. Additionally, you'll find plenty of plug points, snacks and comfortable chairs. Sure, you might not pay for lounge access normally, but you'll easily spend more than $50 for a day in the airport.