There's a place on the application to talk about any optional supplements you are sending [I believe it's on the last page of the online app, but don't take my word for it, I haven't looked at it since October

] I sent in a CD of my band along with a list of shows we have played and also the research paper I wrote for Intel STS. My guidance counselor included a resume and recommendation from the PI of my lab with all the school forms. So there's plenty of ways to send stuff. MIT likes to see varied kids so send what you think will help differentiate you.