Last of vegetables, sweet potato (4)
I believe the answer is:
spud
'potato' is the definition.
(spud can informally mean potato)
'last of vegetables sweet' is the wordplay.
'last of' says to take the final letters.
'sweet' becomes 'pud' (pud is a kind of sweet).
The last letter of 'vegetables' is 's'.
's'+'pud'='SPUD'
(Other definitions for spud that I've seen before include "short, stocky person" , "Spade; potato (slang)" , "Vegetable" , "Weed spade" , "veg" .)