Amy
It is really hard to find a "most" popular one because student body here is huge and there are countless options in clubs and activities. But generally speaking, athletic activities and various parties are popular among most people.
Greek life is not that valued here as it is in private universities. A lot of students are not at all interested.
On weekends, some people go home, some do the laundry and study, some hang out and have fun (there are good places to go in Westwood, Santa Monica, and downtown LA ), some just sleep. For example my roommate spends most of her weekends sleeping and the rest of time watching shows if she does not have homework to do.
As far as I am concerned, I sometimes to to parties and club meetings.I spent most of my weekends studying and working in our most popular dinning hall on campus. I meet friends and talk to them by grabing meals and studying together. Because I love shopping and eating, I always try different stores and restaurants on and around campus.
Peng
The most popular activity is of course the great Beat SC bonfire rally, which is held annually on Wilson Plaza.
Cynthia
I would say that all the groups like USAC and GenRep that focus on representing the student body and organizing campus events are pretty popular and competitive to get into. I am involved with ICARUS Contemporary Dance Company which is the most low key dance group- we practice about 6 hours a week and have on campus performances as well as exhibitions at some dance competitions around the area. There a tons of dance groups, most of them are hip hop, which I don't do, hence the involvement with ICARUS haha. I was a member of Best Buddies (a club to integrate those with intellectual disabilities) last year and am now in Active Minds (a club dedicated to erasing the stigma of mental illnesses and promote mental health).
Athletic events are pretty popular, and tailgating with a group is always fun. Football games are easy to get to without a car because of a bus service you pay for with the Den Pass (if you plan on going to more than 2 football games or basketballs games, GET THE DEN PASS! it's so worth it, and you get a free shirt!).
Now, the party scene- thursdays are insane. not really in a good way... basically, frats have a "quarterly" (huge themed party) each quarter, and they always happen on thursdays. So there are usually multiple quaterlies on each thursday since there are 19 frats and only 10 weeks a quarter. if you have friends in the frat, it's a lot more fun, but otherwise, it's just a huge sweaty cramped mess and you usually have to pre-game since they hide their good alcohol, and you need to show an id to BUY alcohol from their bar. Any other night is usually kickbacks at frats or parties at apartments. So you need to know people. Thursdays, you can walk into any frat and hope for the best haha.
If parties aren't your scene, there are free movie nights at Ackerman grand ballroom or you can go into Westwood with some dorm friends and get Diddy Riese, or a restaurant, or shop. There is always something to do!
Michelle
There's so many student organizations/groups on campus that no one group really has the upper hand in popularity. Like I mentioned before, you find the group that interests you most and you make the best of your college experience and career. Student organizations span across a spectrum of choices, ranging from very academic to very social. It really all depends on what you're looking for, because you will definitely find it at UCLA. For example, there's a yo-yo club, several capella groups, pre-health clubs, tutoring clubs, campus events commission (planning large scale events for the entire student body), sustainability, community service, many religious groups, and the list goes on. There's a club/organization/group for about almost anything you can think of.
Justin
Although Greek life is not a huge percentage of the student body at large, it is a huge percentage of the white, upper middle class, suburban demographic, which itself is a minority. Like I mentioned, every ethno-specific/national/religious group breaks off into fragments and the remainder (something like {4a082faed443b016e84c6ea63012b481c58f64867aa2dc62fff66e22ad7dff6c}20 or less) go Greek. The Greek system here is really just a support system for the minority of students who haven't found an ethno-specific/cultural group to belong to. Not trying to make them sounds like victims, but in this context they are a real minority, so... take from that what you will.
Tanaya
I love planning concerts with Hip Hop Congress, the committee I'm part of in the Cultural Affairs Commission office (which is part of USAC, the UCLA student government). We've brought T.I., Xibit, Living Legends, Ghostface, etc... It's a lot of fun and gives me the experience I need to get a job in PR! The Undie Run is amazing... it's on each Wednesday of Finals Week, and it was my first time doing it this past Wednesday... I had an amazing time, and I regret not doing it before! Thousands of UCLA students (most are drunk) run from Westwood to the Royce Quad in their underwear at midnight while doing the 8-clap and bashing on USC... it's an amazing time that makes you really feel like one with your campus!!
Jason
You asked me if fraternities and sororities are important here. Let me put it to you like this: if YOU think they are important, this is the school for you.
But there are also plenty of other diverse groups, almost anything you could want to immerse yourself in. And being in Los Angeles gives you access to nearly any activity that you can enjoy anywhere else.
Matthew
The most popular student groups on campus are ethnicity-based organizations, though many other groups exist revolving around sports, hobbies, and other competitive events. I am involved with the rock climbing group on campus, and we don't do much other than frequent the rock wall at our fitness center! Students usually leave their dorm rooms open, and the residence halls are very social and friendly. My closest friends are a combination of high school friends and people I met on my dorm floor. If I'm awake at 2am on a Tuesday, I'm probably playing poker with friends. Fun traditions include the bonfire rally before the USC football game, and the Undie Run during finals week each quarter. People party on a regular basis, with most parties revolving around the fraternity and sorority life. I spend all of my weekends working, but there are plenty of things to do when around campus. There is a whole city just off campus, with lots of food, entertainment, and stuff to do.
Leah
There are countless activities to do at UCLA. The majority of campus is REALLY into sporting events. Basketball and Football games are usually sold out. There are also alot of music and theater performances, such as A Cappella festivals, choir concerts, and the UCLA Live season. UCLA is also 10 minutes from the Geffen Playhouse, which houses many incredible productions.
UCLA has a really active social life as well. Students often leave their doors open in the dorms, or hang out in the floor lounges so the majority of a first-year's friends live in their building. Something that is unique to UCLA is that all of our dorms are on one hill, rather than spread out over the whole campus, so if you have a friend that doesn't live in your building, they are at maximum about 3 minutes away from you.
UCLA has a huge greek system, but its also very laid-back. There is no pressure to join, and those who are in it are not considred more popular or less popular than those who aren't. Like I said before, UCLA doesn't have cliques. The greek system is incredibly fun though. Our social calendars are constantly full, plus, we are very close to the sunset strip, an excellent place to hold off-campus events, such as formals or date parties. It's a really great expereince.
People here party mostly on Thursday nights, but also on Fridays or Saturdays if the fraternities or sororities are having special events.
For those who don't prefer to drink, Westwood has 7 movie theaters, not to mention the free sneaks and $2 movies on campus.