My son has been working over 30 hours a week at a nearby grocery store since he turned 16. He loves his job and wants to continue to work these hours. He's not interested in pursuing any after-school activities, other than his job. When applying for college, will he be overlooked simply because he has very few high-school activities on his application? He is averaging a 3.45.
The fact that your son has been working so much shows that he is a hard worker and that he isn't lazy by any means (which looks great to colleges). However, most colleges are looking for students who have experience in a lot of areas -- students who can prove that they are ready for the many challenges college offers. They want to know that a student will be able to manage his time wisely and that he will get the most out of his college years. I would advise him to reduce the amount of hours he works a little bit to pursue some more activities. I don't think, however, that he has to limit himself to school activities.
Sometimes, school activities aren't what a student is interested in, or don't fit in with his schedule. Instead, maybe he could start his own club, which would really show off his leadership skills, or volunteer his time at a place he finds interesting. So many students think that they are limited to what is being offered and don't realize that they can start their own clubs, businesses, etc. Colleges look for self-starters, and I think he'll be happier going through life playing by his own rules. His hard work is impressive; however, it may look a little one-dimensional to college admissions offices. If he can also bring his GPA up to a 3.5, he will be eligible for many more scholarships in the future.