Rep brings beer into ship alongside island (8)
I believe the answer is:
salesman
'rep' is the definition.
(I've seen this before)
'beer into ship alongside island' is the wordplay.
'beer' becomes 'ale' (type of beer).
'into' means one lot of letters goes inside another.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'alongside' means one lot of letters go next to another.
'island' becomes 'man' (the Isle of Man is an example).
'ale' inserted within 'ss' is 'sales'.
'sales'+'man'='SALESMAN'
'brings' acts as a link.
(Other definitions for salesman that I've seen before include "Amen, lass, to the seller" , "He's a seller" , "Fermented honey drink" , "He sells strange lean mass" , "He sells lean mass, oddly" .)