Contain everything in bag (7)
I believe the answer is:
holdall
'bag' is the definition.
(holdall is a kind of bag)
'contain everything' is the wordplay.
'contain' becomes 'hold' ('hold' can be a synonym of 'contain').
'everything' becomes 'all' (I've seen this before).
'hold'+'all'='HOLDALL'
'in' acts as a link.
(Other definitions for holdall that I've seen before include "A large soft travelling bag - stuff everything in" , "Handled bag" , "Large case, with handles" , "Large strong bag with handles or shoulder strap" , "retainer" .)