Junky lacking caution emptied twenty bags (6)
I believe the answer is:
trashy
'junky' is the definition.
(I've seen this in another clue)
'lacking caution emptied twenty bags' is the wordplay.
'lacking caution' becomes 'rash'.
'emptied' means to remove the middle letters.
'bags' indicates putting letters inside (bag can mean secures or steals).
'twenty' with its centre removed is 'ty'.
'rash' put into 'ty' is 'TRASHY'.
(Other definitions for trashy that I've seen before include "Cheap and badly made" , "Cheap and nasty" , "Shy art - rubbishy" , "Shoddy or ganger" , "Cheap and worthless" .)