While you may not have found an extracurricular activity of great interest, consider subjects that you might be interested in. This year, I worked with a senior who had very limited extracurricular activities to speak of. However, he was always interested in astronomy and hoped to have that as his college major. He had done a great amount of investigation outside of school and was able to design an independent study course in astronomy during his senior year. The independence and initiative he displayed did, I believe, somewhat compensate for his lack of structured extra-curricular activities. Happily, he was accepted to his first-choice college.