Quality, not quantity, is key. Colleges look for talent, dedication, motivation, and accomplishment. A student who spends a great deal of time and energy on one activity is usually more appealing than a student who joins dozens of clubs just to build up an application. Colleges want interesting, devoted, dynamic people who know what they love and pursue it.
Extracurricular activities need not be confined to school. In fact, colleges are often quite impressed with students who take the initiative to do something not readily offered to them, such as meaningful community service, employment, or creative writing. Identify your talents and interests and pursue them thoughtfully.