Inside of that envelope was a written invitation to Naruto and Hinata’s wedding ceremony.
Kakashi had already filled out his RSVP form to say that he was going, and added in a congratulatory message. Normally, that was all one needed to do for weddings, but Kakashi had one more task at hand.
The task in question was to rearrange the Mission Roster to make sure that all of Naruto and Hinata’s invited guests –especially their close friends– could attend the wedding without any mission’s getting in the way of their schedule.
It was mostly a headache because Naruto and Hinata’s comrades were all shinobi that were very active in the frontlines of the shinobi world. They were all first rate ninja, and always being handed new missions whether day or night.