I am starting to apply for a job. Do I need a resume?

I am 17 years old and I will turn 18 at the end of august. I am taking half days next year during my senior year so I can work after school. I was just focusing on school and my grades this year and since I got all straight A's during my high school years. I'm going start to apply since I can work over the summer and all of next year. I have no experience working but do you need a resume? I was in band, marching band, jazz band, and NHS and I did volunteer work while I was in it until I moved. Should I list that stuff? What all should I list? What about grades?