100% guaranteed (2,3,3)
I believe the answer is:
in the bag
'100% guaranteed' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for in the bag that I've seen before include "Sacked" , "almost secured" , "Where mail may be" , "Made secure or certain, informally" , "As good as done" .)