At all post offices I have been so far: ink for the stamp used for signing documents, a pad that goes under the paper so the stamp will come out correctly and papers for cleaning the ink from the stamp after using it.
Incidentally, for the next three days I won't be posting anything --nothing serious: I'll be out of town and without a PC.
For a bigger version of this picture both in color and black and white, check my "Japan Arekore" set on Flickr).