Secret things ultimately rile drunk girl (9)
I believe the answer is:
esoterica
'secret' is the definition.
(I know that esoterica is a type of secret)
'ultimately rile drunk girl' is the wordplay.
'ultimately' indicates one should take the final letters.
'drunk' becomes 'sot' (both can mean someone who drinks too much).
'girl' becomes 'erica' ().
The last letter of 'rile' is 'e'.
'e'+'sot'+'erica'='ESOTERICA'
'things' acts as a link.
(Other definitions for esoterica that I've seen before include "Arcane items" , "obscure knowledge" , "collection of specialist stuff" , "Mystic objects" , "Mysterious or secret things" .)