Let's see - Must haves for Art Clay.
1] a plastic roller for rolling out sheets of clay
2] some of the teflon sheets to work on
3] clay form and syringe form of ACS
4] A method for firing your work
5] miscellaneous tools to texture and work the clay
6] one of the books or videos so you know how to get started.
This is the minimal answer - I will post several more working up the scale. I also recommend the forum thread on tools.