Suitcases are a way for the player to carry folders in them. One suitcase can carry up to 8 folders, the same as the Filing Cabinets. Rightclicking with the suitcase in your main hand will open up the GUI. Only folders can be transferred in and out of this inventory.

When held in either hand, suitcases can pick up any dropped items on the ground if a folder within the suitcase's inventory is able to carry it.

Shift right-clicking an opened filing cabinet with an empty suitcase will transfer the entire contents of the filing cabinet to the suitcase, and vice-versa (This only works if one of the two inventories are empty).

Suitcases also comes with a tooltip mentioning a slot index-- This is the index that is currently focused on a slot in your suitcase, where a folder may or may not exist. You can cycle through the indexes by scrolling the mouse wheel while crouching. If a folder exists at this slot location and it can place blocks, then the suitcase will place blocks when right-clicked with. Otherwise, it will fall back to just opening the suitcase's inventory.

Suitcases also have some cross-mod interaction with Botania, implementing the IBlockProvider to provide blocks to items like the Astrolabe to build with. Better builder's Wands may or may not hook into this implementation as well.