A package is an item that can store up to 6 stacks worth of items within itself.
Can be mailed.
Obtaining
Packing
Package is created by packing items into a paper box.
Mailing
Packages can be received by mail as a result of a service crafting or from another player.
Loot
Lost mail packages can be found on a collapsed mail hub or dropped from a charred pigeon.
Usage
Opening
Packages can effectively condense 6 slots of items into single slot, thus they are quite handy as a cheap, single-use backpack.
Info
Using the item in hand will open an interface where stored items can be seen and removed from their slots.
Player can open and close the interface however many times they want, but removing any item will trigger a "break-ready" state, which will be indicated in GUI by red color. Closing the interface in this state will destroy the package and remove all contained items from it, placing them in player's inventory, or dropping them on the ground if no space is available.
Heads up!
Unpacking a package has a 50% chance to return a paper box.
Placing
When used on the block while sneaking, package will be placed as a block.
Breaking a placed package will drop intact package item, with items inside.
Breaking it while sneaking will destroy the package and drop stored items on the ground.
Automation
Dispenser can place packages and a piston can destroy it when pushing, dropping the items.
Sealing
Package can be sealed with a seal stamp, creating a sealed package.