You may want to mention in your résumé as well as in your cover letter that your portfolio is available upon request.
Always bring your portfolio to interviews. When the employer begins to ask questions about your résumé, you can use your portfolio to support your responses.
For example, the employer might say, "I see that you have worked at your school newspaper. What were your favorite writing assignments?" You might reply, "My favorite assignments included this health article (show article in portfolio) that required a lot of research and this creative writing piece (show article) that I wrote for a special edition."
Never leave your original materials with an employer. Offer to let the employer make copies before you leave or offer to send copies of the materials as a follow-up to the interview.
You need to continue to update and add information to your portfolio. Every day (or at least once a week), make notes in an achievement diary about projects or ideas you have worked on since the last diary entry. Save copies of materials you have written as well as notes about decisions you have made that had positive results. Include anything that you think might help you in a future job search.