There are 8 wooden cubes and 8 cardboard "cubes" in the box.
I suppose these are meant to do the same thing, i.e. the wooden cubes were added later to replace the cardboard "cubes" (which were already on the token sheet), simply because they are nicer, right?
From the rule book: "The Inland Port includes three different ways of tracking the goods in your warehouse: the front or the back of the goods counters, or the wooden cubes. Simply use the method you prefer."