Hopefully no one will read into this wrong. I have quite a lot of respect for cap, JrROTC, and scouts. But for those who aren't into those, don't believe for a second that they are the only activities that best prepare you for the academy or military service. They aren't. You can gain just as much following, leadership, team building, and other traits the military is interested in from many other activities. The 2 sport varsity player, marching band member, club leader, class officer, etc... Can learn and experience just as much. And the academy knows this; which is why they don't give you more points for being in cap or JrROTC than they do the president of the national honor society, class vp, athletes, etc..
I'm not writing this to down play cap. I'm writing it because there are those who will join certain activities believing that it is better or helps them more than a different activity. It won't. It doesn't take years in cap or JrROTC to learn military specific things like discipline, marching, saluting, following, etc... 80%+ of new cadets learn this quite easily and have never been in cap, JrROTC, or scouts. So definitely join cap if that's what you want. Join the marching band if you want. Definitely do sports. But whatever u do, Excel at it and attain leadership positions in it. Best of luck.