As an initial matter, I would say you're on the right track by even thinking about these questions. Everyone's experience / path to law school is different, and I think that's OK. In other words, there is no one set of extracurricular activities that is going to make or break your application.
That said, there are some general themes you might consider following (this list is by no means exhaustive). Do something that helps you hone your writing ability, whether that be a creative writing club, pursuing an honors thesis at your undergraduate institution, or something else. Do something you're passionate about--a big part of the law school application process is the essays, and if you've pursued a passion, it's going to be much easier for you to sound interesting and committed when you write your essays. I went to law school with, among others, a piano performance major, a voice major, and a physics major; none of them had typical law school trajectories, but I'm sure they stood out as interesting candidates. Do something that gives you a chance to sharpen your leadership skills--just like undergraduate schools care not only about what groups you were in in high school, but also what positions you held in those groups, law schools (I think) care about the same stuff from college.
So as not to only give you general advice, I'll list a few of the things I was involved in most as an undergraduate. I was on the executive board of a college political group and my fraternity, I was a board member of the Undergraduate Hearing and Appeals System (it served a student disciplinary body, and the board was composed of professors, staff, and students), and I participated in at least one intramural sport every term.
Again, there is no one recipe for success. It's good that you're thinking about these questions now, but my advice, above all, would be not to let yourself be so focused on checking boxes for a possible law school application that you forget to experience college. With mounting pressure on undergraduates to do well to position themselves for graduate degrees, it can be easy to lose sight of the fact that college should be a time in which you grow professionally and personally, not to mention having a ton of fun.
Hope this helps,