There's a lot of confusion about what colleges are "looking for" in terms of a prospective student's outside-of-class activities. In order to be competitive, must a student be a world-class pianist, a star athlete, and the founder of a non-profit that raises hundreds of thousands of dollars for Haitian orphans? No. But schools are looking for students who have interests that they pursue with passion and commitment. Those interests can be virtually anything.
As opposed to the days when well-rounded students--those with an assortment of interests--were in demand, now schools are more interested in angular students--those with narrower interests but who pursue them in greater depth. Instead of well-rounded students, today, colleges are looking to create well-rounded classes. An environment populated by a diverse group of people is both conducive to learning and just plain fun. To this end, schools try to recruit students who represent a variety of interests, experiences, talents, and skills as well as geographic, racial, and cultural diversity.
So, what's a high school student to do?
Start exploring a variety of activities in the first year or so of high school, in order to find things they like; then, they can dive deeply into those activities during their junior and senior years.
Think of extracurriculars as a broad category, including sports, music, visual/performing arts, community service, paid work, participation in interest clubs, student government, tutoring, caretaking of family members, and so on.
If your interest is solitary or intellectual, find a way to make it more concrete. Let's say you're a politics junkie--how will you be able to communicate that effectively on a college application? Any number of ways: you could write a political blog, start a YouTube channel, create a school club, volunteer to work on a political campaign, write a politics column for the school newspaper, take a community college course in political science, etc.
Use your interests as a way to gain leadership experience. For example, can you rise to be a team captain or club president, manage a large project at school, tutor or mentor younger kids?
Ultimately, your extracurriculars, along with your essays, are an important means of helping colleges get to know who you are beyond your grades and scores. So try things and figure out what you enjoy--whatever it may be--and just do it!