A "unique item" can be anything as long as it fits completely on the card and you don't use the same thing twice. Two items are considered the same for this ability (which is to say, one of them is not unique) if they have the same or nearly the same shape, size, and colors. For example, a 2020 U.S. quarter is the same as a 2021 U.S. quarter, but it's not the same as a Canadian quarter or a U.S. nickel. If all players can't agree, you may ask an outside person for a final determination.