It's not too early to be building your high school resume. Begin by keeping track of the activities listed below in a document, in a noteboook, or whatever works best for you. Most word processing programs have a template gallery which includes templates for resumes. Here is where you can find a Google Doc resume template.
Some important information to include:
Education
Work experience
Community Service
Awards, Honors & Certifications
Skills
DON'T ADD TO YOUR RESUME- but be ready with 3 references with name and email.
Both of these resumes are a bit longer, typically it's a good idea to try to keep a high school student resume to one page.