Honest answer–and I know a bunch of people will criticize this point–quit every sport besides 1. Are you going to be a recruited athlete? If yes then focus on that sport and you are in. If not having 3 sports does not make you very well-rounded and it puts a huge burden on your free time.
Volunteer work is a good idea. Just like sports tho, you only need 1 volunteer service to be well-rounded. Volunteering to help underprivileged youth sounds like a really good activity btw.
You should look at other activities as well such as a foreign language or photography club. Maybe start learning about technology or learn some basic programming. Or learn about the stock market and trading. etc.
Simply put diversify yourself.