Congratulations to your great academics thus far.
You’ve gotten good, specific hints already.
Let me just add, whatever cause you get involved with (regardless if it’s related to your possible major), pick something that you feel strongly enough about, and have the means, to carry through for the next 2 1/2 years.
ECs may be valued more, if they imply serious commitment, not just another one-year “check box” thing.
(I know of rising seniors who just NOW are going to start volunteering for soup kitchen, as they are working on their college essays. While I appreciate their time, I hope their motivation is solely community service, not to impress admission counselors.)