Most residency programs require at least 3 LOR's with your application, not including your dean's letter. As a general rule, these should be from faculty in the field you are applying in, although letters from other specialties and/or research mentors are also acceptable. At least one of these letters should be from your school's chairman of the department/specialty you are applying for. You can submit up to 4 LOR's to each program through ERAS, and you don't necessarily have to send the same ones to everyone.
A letter from an extracurricular activity is probably worthless, although there is nothing wrong with including your experience in your CV.
Hope this helps.....
