You know you have to have one. You're a student, not someone who's been in the workforce full-time for ten years. Volunteer work, school activities, and other experiences are great for high school students and recent graduates to put on there. Once you've been out of school awhile, that won't be appropriate anymore, but for now, use whatever you've got. It's still your accomplishment.
School activities can have their own category.
Don't forget to mention all offices you've held or responsibilities you've taken on. In general, just put on everything you're proud of.