Volunteer to remove top from box (5)
I believe the answer is:
offer
'volunteer' is the definition.
(I know that volunteer can be written as offer)
'remove top from box' is the wordplay.
'remove top' means to remove the first letter (I've seen 'removes top' mean this).
'from box' becomes 'coffer' (I've seen this before).
'coffer' with its initial letter taken off is 'OFFER'.
'to' acts as a link.
(Other definitions for offer that I've seen before include "Hold out, tender" , "Put forward" , "(Suggestion of) gift" , "Tender, make bid for" , "Volunteer -- proposal" .)