Contain everything in case (7)
I believe the answer is:
holdall
'case' is the definition.
'contain everything' is the wordplay.
'contain' becomes 'hold' (synonyms).
'everything' becomes 'all' (all things).
'hold'+'all'='HOLDALL'
'in' is the link.
(Other definitions for holdall that I've seen before include "Large bag (no need for another?)" , "Handled bag" , "Capacious bag or basket" , "Item of luggage" , "Large strong bag with handles or shoulder strap" .)