By the sound of it, ready for holiday agreement (4)
I believe the answer is:
pact
'agreement' is the definition.
(a pact is an agreement or deal)
'by the sound of it ready for holiday' is the wordplay.
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'ready for holiday' becomes 'packed' (having suitcases packed).
'packed' sounds like 'PACT'.
(Other definitions for pact that I've seen before include "Alliance" , "Treaty, formal agreement" , "'Accord, treaty (4)'" , "deal" , "International treaty" .)