Sticker back on a container (7)
I believe the answer is:
gelatin
'sticker' is the definition.
(gelatin is sticky)
'back on a container' is the wordplay.
'back' says the letters should be written in reverse.
'on' becomes 'leg' (cricket term, fielding positions).
'container' becomes 'tin' (tin is a kind of container).
'leg' written backwards gives 'gel'.
'gel'+'a'+'tin'='GELATIN'
(Other definitions for gelatin that I've seen before include "Colourless protein - edible jelly" , "Tag line (anag.); glue" , "Substance used in glue and cooking" , "Jelling agent" , "something gluey" .)