Caviare? Very thin gourmand has the lot (10)
I believe the answer is:
everything
'the lot' is the definition.
(I've seen this before)
'caviare? very thin gourmand has' is the wordplay.
'has' indicates the answer is hidden within the clue.
'EVERYTHING' is hidden within 'caviare very thin gourmand'.
(Other definitions for everything that I've seen before include "The whole shebang" , "the works" , "great deal" , "All that is; life in general" , "All items" .)