Students enjoy the city and the campus on weekends. There is so much to do within a train ride (and that includes somerville and cambridge).
Clubs are not competitive and I don’t think you will have any problem joining any one that interests you. There are clubs to cover any interest - professional ones (for your major), cultural ones (things like chinese culture), hobby ones (cooking, video games), service/charitable ones, etc.
Boston in general is a pretty big drinking town, but don’t expect to get into the tons of bars with a fake ID (the city makes too much trouble for places that let you in underage). The campus doesn’t have a big party atmosphere.