From what I know the Packet Office (still have zero idea why it's called that), otherwise known as Inbound Clerical, deals with switching around IB trailers, announcing IB freight flow numbers, switching item dispositions (conv to non-con, EW to TW, that sorta thing). They work very closely with dispatch, the yard drivers, the IBGL and the IB team. There's probably a lot more that I'm not stating, but I don't interact with them much on a daily basis.
You pretty much got down what TSS does. They also do rounds and check on the security items and manage the movement of trailers around the yard, but from what I hear from most of my fellow TM who back-up, it's a whole lot of just sitting around in the guard shack.