Says it's in the bag! (8)
I believe the answer is:
declares
'says' is the definition.
(declaring is a kind of saying)
'it's in the bag' is the wordplay.
I cannot quite understand how this works, but
'it's' could be 'es' ('e' can mean 'electronic' which is similar to 'IT') and 'es' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for declares that I've seen before include "makes confession" , "States emphatically" .)