Marco Polo's treasures
I don't have a costume idea for you, but I did use this idea that the students enjoyed.
Take a wooden box (the older the better), line it with a rich-colored tablecloth, and fill with items that Marco Polo would have brought back from his adventures. I included some silk cloth, whole spices in old-looking containers, perfumes, rice, etc.
The students were divided into groups, chose an item without looking, and described and shared what the item was used for and why it was important enough for Marco Polo to bring back.