The Package is a key item that appears in Paper Mario and Paper Mario: The Thousand-Year Door.

In Paper Mario

The Package can only be obtained once Mario accepts one of Koopa Koot's many favors. Mario must head to Gusty Gulch and get the Package from one of the Boos there. Mario must wait a little while to receive the Package and once he does, he can take it back to Koopa Koot to be awarded with a coin.

In Paper Mario: The Thousand-Year Door

"An item Goldbob asked you to deliver to General White."
― Description

In this game, the Package is part of a trouble requested by Goldbob of Poshley Heights. He requests Mario to deliver an important Package to General White. However, this involves going on another wild goose chase for General White until the Package can be delivered to him.