I'll go with ceramic pots for orchids as a major supply need. Many orchids are or become top heavy and the only way to keep them safe is being in a decorative pot of some sort. I have a number of the fancier glazed pierced pots and a number of terracotta pots made for orchids (a much cheaper alternative).
Next on my list is bark/coconut husk chunks for potting and then fertilizers.
And then there are the artificial lights. Though that isn't really a 'supply' more of a capital expense.