Shell Earrings

Doopliss (disguised as Zip Toad at the time) steals the Toad Waitress's Shell Earrings  on the Excess Express during Chapter 6 of Paper Mario: The Thousand-Year Door. The Shell Earrings are meant to be a part of the Shadow Sirens' plans to create an explosive form of Nitro Honey Syrup. To do so, they need the Nitro Honey Syrup plans from the Businessman's briefcase, a source of gold (Toodles's Gold Ring was what they chose), and a source of seashell calcium. However, Mario puts an end to their plans, retrieving the lost items. If Mario gives the Shell Earrings back to the Toad, she gives him a Star Piece.

According to in-game descriptions and the Toad Waitress herself, her ex-boyfriend gave her the Shell Earrings, who apparently talked to her via telephone shortly after Mario returned her earrings. Mario may have actually met this ex-boyfriend, because talking to a certain unnamed Squeek (who often tells Mario of his many love relationships) after beating Chapter reveals that he was once in love with the Toad Waitress. Squeek also wonders if the waitress still cherishes them as he spoke to Mario.