Crate
From PinataIsland.info, the Viva Piñata wiki
Crates can be purchased at the Post Office. After you place the crate in your garden, you can pack up to five items (anything found in the game, including piñatas) into it and ship it off to another player via Xbox Live. You can even pack up a sour pinata and ship it off to an enemy.
You can pack pinatas, eggs, plants, seeds, candy, decorative objects, helpers, houses, produce, and money into a crate, but you can only pack one kind of object in a single crate.
The recipient can't tell what's in a crate until they open it.