Since you are not selling the work in your portfolio, would you still be allowed to use projects that included copyrighted materials (songs or dialogue/audio, for example) after you've graduated as long as you credit them? Or would you have to ask for permission/pay a fee?
Yes, you can include copyrighted content as part of your portfolio, as long as it's credited and clearly labelled as student work. You should probably consider limiting distribution (i.e. not posting it to the open web). It would be a good idea to let your potential client/employer know somehow that you understand how copyright works, and indicate that you were using these elements as a student, underlining that you would not violate copyright yourself by trying to sell works without getting permission from the copyright owners.