Mentioning that you have been active in clubs or student government is good, particularly if you can show evidence of leadership or commitment. For example, it helps to have been club president or on student government for three years. Keep in mind that different schools value leadership differently, because the same position varies greatly between high schools. At one school's newspaper, the editor could be the one doing all the work and making all the decisions, while another school paper could be run on more of a committee basis, with less of a leadership role for the editor.
Activities like the debate team, competing in musical or dance competitions or winning a poetry contest look very good on a college application. The more selective the college, the greater the expectations. One school might be happy with a student who played in an orchestra for several years, while another might expect a student to win a competition, be a drum major or play first chair.
Colleges also look at an applicant's work experience for evidence of exceptional perseverance, commitment, work ethic or leadership. It is preferable to have had a job involving some special skill or supervising others, but colleges will take any job into consideration. A student who works long hours to save for college or to help support the family won't be expected to have as many activities in other areas. Admissions officers understand that there are only so many hours in the day.
Community service is an excellent extracurricular activity. Some colleges even place it in its own category, so even a student with a good record in other areas should include some community service experience. Make a long-term commitment to a cause you care about. Most applicants claim some kind of community service. You can stand out by showing that you volunteered because you cared, not just to have something to say on an application.