Graeber's Debt mentions an interesting theory that the first state coinage was actually intended to generate a distributed supply system for military forces without paying attention to the complex logistical details. Pay your soldiers with valueless tokens, demand your subjects pay tribute to you (taxes) with those tokens, and the whole thing works itself out. It has the added benefit that the soldiers don't get stabbed when they try to "requisition" supplies because on the surface it appears to be a fair exchange.
unfortunately I don't. rereading Graeber, I also realize that he never explicitly said "the first state coinage", so now I am uncomfortable with claiming such. he was speaking generally about Chartalist theories of states' early efforts to create markets and presenting a hypothetical situation in which it would be beneficial to do so.
I was only able to find this, which is by Graeber also: I've been told about a theory which postulates that markets came about as a way for generals to get rid of their booty in exchange for items which were more useful than the spoils of war, but I can't remember whose theory that was.