Section of supermarket? I'll say! (5)
I believe the answer is:
aisle
'section of supermarket?' is the definition.
(I've seen this before)
'i'll say' is the wordplay.
'say' shows a homophone (sound like).
'ill' is a homophone of 'AISLE'.
(Other definitions for aisle that I've seen before include "Passage between pews" , "Extension of the nave in a church" , "Passageway between pews" , "Passages between seating areas" , "Passageway between blocks of seats" .)