Items work exactly like markings. If the two people have two different sets of items, they will see the other player as wearing on that's on their own list. If that slot on the list is empty, they won't see any item.
ex:
player 1 has the default hat, a set of horns, and a bubble in their list.
player 2 has the default hat, a bubble, a tutu, and fangs in their list.
player 3 has the default hat in their list.
if player 1 is wearing the horns, player 2 will see a bubble and player 3 will see nothing.
if player 2 is wearing the tutu, player 1 will see a bubble and player 3 will see nothing.
if player 3 is wearing the hat, everyone can see it.