Sailor, on his own, having some seafood (7)
I believe the answer is:
abalone
'seafood' is the definition.
(type of sea snail)
'sailor on his own having some' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'on his own' becomes 'lone' (all alone).
'having' indicates putting letters inside.
'some' becomes 'a'.
'ab'+'lone'='ablone'
'ablone' placed around 'a' is 'ABALONE'.
(Other definitions for abalone that I've seen before include "Edible marine mollusc -- Oban ale (anag)" , "Shell used for decoration" , "paua" , "Ormer, ear shell" , "Source of mother-of-pearl" .)