The boot bag made of this (7)
I believe the answer is:
sacking
'the boot' is the definition.
(being given the boot means being sacked)
'bag made of this' is the wordplay.
I cannot really see how this works, but
'bag' could be 'sack' (both can mean a container) and 'sack' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sacking that I've seen before include "Firing the coarse cloth" , "P45" , "Firing; coarse material" , "Dismissing (from post)" , "made of hessian?" .)