About to have nothing but caviar (3)
I believe the answer is:
roe
'caviar' is the definition.
(fish eggs)
'about to have nothing' is the wordplay.
'about' becomes 're' (regarding).
'to have' indicates putting letters inside.
'nothing' becomes 'O' (looks like zero - 0).
're' going around 'o' is 'ROE'.
'but' acts as a link.
(Other definitions for roe that I've seen before include "A mass of fish-eggs" , "shy animal" , "Caviar" , "eg Caviare" , "Food from fish" .)