Although you can get through security fine this way, it's against FAA regulations to drink alcohol on a plane that isn't served by the crew. You could drink it

Although you can get through security fine this way, it's against FAA regulations to drink alcohol on a plane that isn't served by the crew. You could drink it in the airport legally (I think), but not on the plane. Of course, you may be able to get away with it on the plane anyway, but you'd have to be discreet.