My pledge pin-- it was a symbol of my pledgeship. It is given back to the national before initiation. From initiation on, I had my Pi Phi arrow, not the "Beta" dart pledge pin.
For a long time, I had the pledge ribbons, too-- I don't think that I have them anymore.
I don't have the Beta dart but I do still have the pledge ribbons! Unfaded, oddly enough.
For me, it'd be my pledge manual. Nationals tends to issue different ones in different semesters, so they're somewhat unique to the pledge class. It served as a guide to understanding what my fraternity is about and how it worked.
In contrast, the pledge pins are just returned to my chapter for safe-keeping by the member educators and recycled for each class until they break.