Start with Team Bennett611.
Find time to tell your current teachers about your aspirations. They see the pronounced improvement, maturity, focus from the 2.9 year to the 4.0 year. Teachers talk in the teachers lounge. Probably among the grade level but also by subject area (ie, E, M, Sci). Go on your fact finding mission and figure out who are your 11th grade teachers. Do they have volunteering you can start with, such as summer boot camp for students, etc? Get to know them early? Get on your GC's radar.
CRUTCHES! Take the lead and ask your parents for help. How this may impact DoDMERB and start a file now, making notes what you will need 2 years from now. And of course anything else, like childhood ear tubes, etc. Read all the DoDMERB threads, pay attention to diagnosed or not. You can google the 85 question DoDMERB form, but I caution you i'm just a parent saying what I did. Go to the main source, and big hint - make sure to "Follow" Mr. Mullen on SAF!!!
Plan and execute good/great ACT/SAT scores.
Leadership and achievement in cross country/track for sure. Get on varsity, hopefully captain.
In all major leadership ECs, can you cite project, time frame, budget, summary, who benefit, unit of measure, follow up plans?
For example, "I give pep talks to motivate team members at meets". Meh.
"I organized a car wash for cross country and got football and swim team to join. I cleared it with the Principal and the district to have it in the student parking lot, and 35 people from 3 teams showed up and we washed 100 cars and made $1500 to benefit the American Red Cross and booster club 50/50. Our proceeds are to help defray costs of swim suits, new field equipment, and sweatshirts for the track team. I made a binder for next year and the tennis team and student council want to participate as well. We are thinking to sell donuts in the morning and hot dogs at lunch time for waiting customers." See the difference! (PS - remember to ask your PTSA to donate $ for the donuts and hot dogs!)
You mentioned mowing your neighbor's yard. That is actually a huge deal, IMO. That's classic service to your community, and who better than a neighbor that needs help? Why not start a business, and offer to mow yards and house watch during the summer, such as $10/day to collect mail and move potted plants on the porch, pet sit when neighbors go on summer vacation? You can take a yard sign and advertise in your front yard "Bennett611 your neighbor offering house sitting and lawn mowing! Call xxx-xx-xxx!" or "This yard mowed by Bennett611! Call xxx-xx-xxxx!"and make flyers and put in mailboxes in a reasonable radius from your home, post the flyer on the neighborhood facebook page.
The other way to tell your engagement is time. On your resume, can someone recreate your day? How much time are you spending where? Where are you on any given school day, doing what?
These are just some ideas, hopefully will spark new ideas for you in activities you enjoy. Do NOT worry about "what will make me look good", but rather, what truly motivates and has meaning to you. Your resume will have both "check box" things and major, anchoring activities. It's not the activity, but your ability to answer how have you, through activities and accomplishments (whatever they may be), demonstrated the characteristics that will make you successful at this SA and branch. Did you demonstrated you have the capacity to take the opportunities of this SA/branch and be successful? Why should they bring you to the Brigade?
A parent's perspective.