I know that when you have a boarding pass, and are just trying to get an earlier flight, you can get on a standby list at the gate and wait to see what happens.

However, if you are trying to fly for a lower fare (in the case of filling empty seats on an airplane), can you do this without buying (I assume) a regular fare in advance? I ask because as far as I know, if you don't have a boarding pass, you cannot get through security and to the gate.

I am willing to spend a few days at the airport in this effort, so that is not a problem. To be specific, my plan is to fly from California to Japan.