How do you tell a college all about the many "activities" you've done and currently do, when you're filling out your applications? This falls under the umbrella of what I call "student profile marketing." Why should you do an "annotated" Activities List?
As you may already know, college application forms don't offer active students enough space to list and explain their extracurricular endeavors, jobs, honors, etc. A few colleges (Columbia, Stanford, for example) state in their application instructions that separate résumés and other attachments are not permissible, but for the vast majority of schools, it is quite acceptable to submit an annotated list in addition to the information that you put on the application form itself. Note that if you are applying online but plan to send a separate activities list, you can either email it or snail-mail it separately. You may also be able to upload it into the "Additional Information" section of the Common Application.