Consume entirely (3,2)
(Other definitions for eat up that I've seen before include "43 [TUCK] in" , "Finish course" , "Consume completely" , "Finish one's food" , "Exhaust" .)
'consume entirely' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for use up that I've seen before include "Expend" , "Entirely consume" , "Finish, exhaust" , "Consume (stocks)" , "Exhaust (resources)" .)