Ladies and gents key to replace small coins (5,6)
I believe the answer is:
loose change
'small coins' is the definition.
'ladies and gents key to replace' is the wordplay.
'ladies and gents' becomes 'loos'.
'key' becomes 'e' (I've seen this in other clues).
'to replace' becomes 'change' (changing is a kind of replacing).
'loos'+'e'+'change'='LOOSE CHANGE'
(Other definitions for loose change that I've seen before include "Coins kept for casual use" , "little cash!" .)