I reserve a drawer in my huge, ancient, crickety teacher desk where I have a hanging folder for each student - this becomes their "portfolio." Throughout the school year I place particularly meaningful assignments, creative projects, and important assessments in their "portfolio."
Sorry it's low quality - I blurred out the student names...but you get the idea of how the portfolio system works.
The students know that I keep these and often come to me with something they're especially proud of and ask if it can be included in their portfolios.
At the end of the year, I write a note to each student and add it to their file. I pass out blank file folders to the students and have them decorate them with pictures and words that describe their feelings about 5th grade (hopefully positive!). I then collect the folders and transfer all of the documents in their portfolio to the folder and stick a big rubber band around the whole thing (they get quite fat!).The last couple days of school, I hand out the portfolios and have the students reflect on how far they've come in 5th grade. They choose the piece (or two) that they are most proud of and get to share it with the class. It's an awesome tool in helping them be reflective learners.