As mentioned previously, this section of the application does not have to do with your involvement in leadership/extracurricular activities in JROTC, but rather outside of it. The selection board wants to see your ability to branch out and look for more opportunities other than the ones handed to every cadet in JROTC. Remember, this program requires you to be the best of the best, so you have to prove it. Below I have made a list of the best possible extracurriculars to include in this specific application.
As mentioned by the Air Force themselves, one of the first things that they look for in the selection process is holding a job. A simple, part-time job goes a long way on this resume. It shows your ability to balance JROTC, schoolwork, and another commitment, so this is one of the best things to include on an application. Also, a leadership role is amazing, but not necessary, in this field. If applicable, talk to your employer about the possibly of slightly altering your job title on this application to better reflect the tasks that you demonstrate leadership on throughout the shift. A simple title of "leader", "manager", "overseer", "coach", or "instructor" goes a long way.
Your involvement in a sport/club team is also a good thing to provide on an application. A leadership/captain role on your team is just as good as the part-time job title on your application, but if possible include both. It may sound like a lot of work, but playing a sport for a season of the year shows your ability to take on tasks and adapt to schedule changes that are frequent in an accelerated program such as the Flight Academy.
At NA, simply joining the track team/cross country team is a great thing to include on an application.
This commitment was less stressed by the Air Force as being imperative to include on your application, but, nevertheless, being apart of a simple, monthly volunteer task/project can make your resume stand out tremendously. As an example, I personally volunteered at my church's food collection once a month sorting through donations. Something that simple, that only took up two hours of time on a weekend, makes a great deal of impact not only for your resume but also for your community.