Can't live without grape juice and it's unavoidable (5,4)
I believe the answer is:
needs must
'it's unavoidable' is the definition.
(I've seen this before)
'can't live without grape juice' is the wordplay.
'can't live without' becomes 'needs' (I've seen this in another clue).
'grape juice' becomes 'must' (I've seen this in other clues).
'needs'+'must'='NEEDS MUST'
'and' is the link.
(Other definitions for needs must that I've seen before include "what wine-making does" , "Of necessity" , "Perforce" , "'. . . . . . . . . when the devil drives'" , "It is necessary" .)