Activities do wonders and sometimes more is taught in after-school activities than in the classroom. They teach volunteerism, respect and responsibility, to name a few things. It's a great way to meet friends as well, as be social with them. In addition to this obvious fact, many colleges look at activities and involvement in and out of the school. This could include National Honor Society, Key Club, or athletics, as well as outside activities like working, club sports or volunteering.
Activities can lead to open doors in life like a career or hobby.
Starting sophomore year, I started using an organizer. This helps a lot to keep things straight. Most of all, I try to keep my priorities, and high on that list is friends. If I don't have the time, I make it as best as I can. I know and accept the consequences for not doing something.