Shopping area aboard ship supplies underwear (6)
I believe the answer is:
smalls
'underwear' is the definition.
(type of underwear)
'shopping area aboard ship' is the wordplay.
'shopping area' becomes 'mall' (shopping mall).
'aboard' indicates putting letters inside.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'mall' placed inside 'ss' is 'SMALLS'.
'supplies' acts as a link.
(Other definitions for smalls that I've seen before include "Underwear (colloq.)" , "Undies" , "Undersized underwear?" , "Diminutive items of underwear" , "Diminutive articles of underwear?" .)