When applying for an internship, you should be prepared to supply the following:
It's important to keep in mind that the cover letter is the first opportunity for a potential employer to learn about you, as well as exhibit your writing ability. Effective cover letters convey a sense of purpose, enthusiasm for the position, and demonstrate your knowledge of the employer's goals and needs. A positive first impression requires that your cover letter be concise, and contain zero errors in spelling or grammar. Your cover letter should be customized to fit the position for which you are applying.
This should include:
1) Your educational background, including your area(s) of concentration and relevant coursework;
2) Any significant experiences, including your work experience, volunteer experience (internships, community service), and campus leadership.
3) Honors/Activities/Leadership that highlights skills most pertinent to your internship/career goal.
Writing Sample & References
While it is not always required to supply these with your application, it is helpful to have these items on hand at the interview. Unless specified, choose a writing sample that demonstrates your best work within relevant course material - between 4-8 pages.
Your references should be informed in advance, and chosen from your academic and (if applicable) professional experience. The reference sheet should include: name, title, organization, phone number and email address.