There are LOTS of extra curricular activities. For lower school there are the chess club, history club, choir, drumline, pep squad, Knight guard for boys, etc.
You can pay extra to have music lessons at school or for gymnastics after school.
for middle and high school there are LOTS of sports, cheer, drumline, chess, robotics, national honor society, publications, student council, newspaper, journalism, yearbook, latin club, spanish club, latin team, etc. There are TONS of opportunities for students to be involved. There are more than just these, I can't think of everything.
The administration will help you start a new club or sports team if they don't have it!