I know this is a game and too much forcing real life in a game is not a good thing. But I just found this and it could gives a lot of great ideas to pak maker here...
http://www.wcoomd.org/home_hsnomenclaturetable2012.htm (http://www.wcoomd.org/home_hsnomenclaturetable2012.htm)
In some cases, this list is more fine grained than Simutrans, in other cases it is more generic. I don't think there are vehicles specially made for transporting headgear, a more generic vehicle is used like a box car, intermodal container or swap body. Nor is there some generic headgear factory, but many kinds depending on shape and material from helmets to kippahs.
The ultimate challenge may be to fit just one factory of each kind on a single map without overcrowing it.