Let's see. College admissions....SUCK. It all depends on where you want to go, and keep in mind, you could do everything in the world and still not get into the school of your dreams. For example--Cornell. I have a 4.2 GPA, 1410 on the SATs, am an Eagle Scout, member of NHS, Yearbook Editor, member of two Explorers Posts, have won a ton of awards, and I'm in five AP courses. Yet they wait-listed me. Why? No clue...I like to think it's because they are arrogant, ivy-league peeps who can do anything they want. Anyway, if you are applying to an Ivy League school, I will be honest with you. Grades are nothing. Why? Because EVERYONE who is accepted naturally gets all A's. So, if you don't, you're out, but if you do, it doesn't get you much. So, assuming you get excellent grades and do well on the SATs, extracurricular activities and community service projects are VITAL. You cannot possibly do too much. You are trying to sell yourself to the schools and want to look as well-rounded as possible, so involve yourself in a lot of extracurricular activities. Not to scare you or anything, but this year, especially, college admissions have been a NIGHTMARE. More students are applying to colleges now than ever before. All of the schools I applied to saw acceptance rates plummet as MANY more students applied this year, so many of those schools dropped to acceptance ratings of about 10 to 15%, which is ABSURD. This also means it is tougher to get merit based scholarships, so you do have to work hard in high school. That said, you will get into a good school and they will give you a lot of money if you keep your grades up and get involved in the community...just might not be your top pick. I might add most schools will offer an essay explicitly asking about your extracurricular activities and when you ask teachers for letters of recommendation at the end of your junior year, they will want a listing of all your activities, awards, jobs, and "special experiences" (i.e. did you go to Europe? are you a student ambassador somewhere? etc). Oh...oh...oh...do you possibly want to major in...biology??? That is one of the most popular majors this year...therefore it's tougher to get into that program. By the way...smaller, private universities will treat you nicer than Ivies...like...St. Lawrence University is giving me $84000 is scholarship and will pay for me to study abroad in Australia...
Regardless, good luck sir! To answer your question simply...if you want to go to a really good school and have no extracurricular activities...odds are they won't accept you.