John Travolta's first to get sack (4)
I believe the answer is:
loot
'sack' is the definition.
(I've seen this in another clue)
'john travolta's first' is the wordplay.
'john' becomes 'loo' (both can mean a toilet).
'travolta's first' becomes 't' (1st letter of 'travolta').
'loo'+'t'='LOOT'
'to get' acts as a link.
(Other definitions for loot that I've seen before include "Stolen property" , "Orton play; ill-gotten gains" , "Tool for plundering" , "Steal property (in war)" , "Plunder and ransack" .)