Ask your boss to review you. As weird as that might sound, your boss has experience in the job you're one day going to be applying for. Ask your boss to grab coffee with you before work or sit down for 15 minutes during they day to have a quick exit review about your performance. They can give you invaluable advice about how well you did your job, your work ethic, tips and ways to improve, etc. It's a great opportunity to gain one-on-one time with your boss and take your relationship to the next professional level. You can pick their brain about how they got where they are, where they want to be in their career and how you can get there, too!
Write 'thanks you' notes! Seriously, this small detail is severely over looked. A hand-written thank you note is something that is not only polite, but helps you stick out from the rest of your fellow interns when you're leaving. This small gesture is, to me, not at all outdated and underrated. By just a quick few sentences expressing your gratification to your boss and others you worked with, it shows how much you really enjoyed your time interning for them, you appreciated the opportunity and that you want to keep in contact. Don't forget to write your e-mail on there either so you can keep in touch!
Get contact info from your fellow interns. Whether or not you became BFFS with the other interns you worked with, they're all going down the same career path you are and they're invaluable contacts for your future. I've been told time and time again not to underestimate the power of the people you intern with not just who you intern for. Someday those interns will get jobs somewhere else and by keeping in contact with them they can give you inside scoop on other jobs within the industry and be great references!
Although there are hundreds of tips dealing with how to end your internship on the right note, I think these are three of the most important. Be sure to be giving 110% your last few days because leaving a positive lasting impression will be invaluable for you down the road!
Good luck, Edsters!