I understand that it is advisable to bring a number of invoices from
firms you do business with, rather than just a list of them. That
way, they can see that you have a real business. Also, I believe you
will need your business license, and your Fed. ID tax number.
Most of all, bring lots of money. That place is just fantastic.
Caution, if you are buying gems, bring a powerful loupe. A friend got
some stones that looked great, but when she got them home found that
several had fractures.