Command packet

From Memory Alpha, the free Star Trek reference.

In the 23rd century, the command packet contained a copy of a starship's destination schedule, as well as the Captain's taped last orders. The packet itself was a black envelope emblazoned with the vessel's assignment patch and it was kept in the Captain's personal safe. A commanding officer would have it on hand during court martial proceedings, such as a preliminary hearing, but the packet would not normally be taken off the ship. (TOS: "What Are Little Girls Made Of?", "The Tholian Web", "The Menagerie, Part I")

It is probable that the command packet contained other documents besides the itinerary. One document likely included would be the orders that assign command of the ship to her captain.