At my college you rented the gowns, or at least that was the default, but I think the cap was bought and yours to keep. Also, as a souvenir, the tassel, which

At my college you rented the gowns, or at least that was the default, but I think the cap was bought and yours to keep. Also, as a souvenir, the tassel, which is decorated with a charm showing the year graduated, is also always (obviously) yours to keep. It’s very common in America for young people to hang that tassel from their car’s center rear-view mirror.