You do the things, you WANT to do.
There is no magical checklist....... "DO THESE ITEMS AND YOU GET ACCEPTED TO THE ACADEMY". It doesn't work that way. Just like the kid who never played a sport in their life; gets on the football or basketball team their senior year so it will "LOOK GOOD" on their college resume. The academy isn't stupid. They've got a little bit of experience appointing people to the academy. It is SO EASY to see an individual doing something to make their resume look good. If you're looking to "FILL A SQUARE", then this forum isn't the right place for you to ask such a question. This forum is for those who want to EARN an appointment; and want the academy to appoint those most deserving.
Whatever you decide to do on the weekends, do it because YOU WANT TO. Then, while you're doing whatever it is, find opportunities in that to demonstrate leadership, team building, service to others, etc. EXAMPLE: Part time job; Volunteering Meals on Wheels; Church League Basketball; coaching kids soccer at YMCA; organize you x-country/track teammates to do additional training; (Schools are limited on practices, athletes can practice on their own); etc. WHATEVER YOU DO, do it because you want to. PLUS, each of those examples, and ANYTHING you think of, you'll be able to find ways in it to show "Leadership, team player, service to others, etc". Just make sure it's GENUINE and not just trying to "Fill a Square". You ALO can see that coming a mile away.