jrosedal, Stanford University '18
This is hard to answer, since the students here are so diverse in their interests. One activity that's popular not just in membership numbers but with the entire student body is the Leland Stanford Junior University Marching Band (LSJUMB), or just The Band. The Band is a great community of spirited students who come together to make everyone else's lives great (and sometimes awful, when it's 3:00 in the morning and they're doing a victory lap around campus because we beat Cal). You don't need to know anything about how to play an instrument to join; you can learn after, or you can just yell a lot. Seriously, it's great. I'm not in Band this year, but hopefully that'll change soon; from what I've heard from my friends who are, it can only be described as an Experience.