This is DEFINITELY illegal so I'm going to be as generic as possible for my own protection

I once had an 8:00am domestic business flight for a client-paid-for meeting. The next flight wasn't until almost noon, and it was a new job, so I could NOT miss this flight. Of course, this was the one time my body decided to over sleep on a travel day.

There was really no feasible way to make it, but I figured the least I could do was give it my best effort anyway. In my mind, I could say I did everything I could. So that involved driving like a maniac - close to 100mph on open stretches - to the airport, pulling into the park-n-ride about 40 minutes before takeoff, sprinting between catching my breath on shuttles, somehow making it through security pretty quickly, and arriving at the gate after the flight had closed. BUT, the plane was still there. As I was pacing recovering from my latest sprint and trying not to have a heart attack, I spotted a maintenance worker in a yellow vest walking towards the jet bridge. I casually paced behind him, and lo and behold he scanned his badge and opened the door. Amazingly, my brain told me "follow him!", so as the door was closing, I pretended I was where I was supposed to be and just casually walked behind him down the jetway, roller bag in-hand.

As I got to the plane, the flight attendant stopped me: "Sir..." ...full-on heart attack approaching... "...we're out of overhead bin space, we're going to have to gate-check that bag." In my best acting, I pretended to be very mildly annoyed but compliant, then just proceeded to my seat. Someone was in my reserved exit row aisle seat (because I wasn't supposed to be on the plane, obviously), but the middle right next to him was open, so I sat there as if it were my seat, took the flight, and life went on.

Oh, and I called the airline later to report the missing flight credit and they corrected that, too, and apologized for the error.