There are few instances when you get as close Charles XII as when you hold in your hand a letter which contains his notes. A particular group of such documents which contains his own "illustrations":
A doodle made by Charles XII usually (in my experience) contains weapons (axes, halberds and such) and field-works. This example would seem to be slightly more civilian in character (a lot of Latin numbers) and an even today often used vulgar term for urine ("piss"). The Royal unhappiness may have had something to do with the content of letter - the letter from Col. Schlippenbach and the attachment from Lt. Col. Romanowitz vividly explains the poor state of the soldiers due to the cold and the various hardships suffered.
Source: Riksarkivet, Stockholm, Skrivelser till Konungen. Karl XII:s tid, vol. 23