Staff canteen's opening in month before winter sale ends (7)
I believe the answer is:
sceptre
'staff' is the definition.
(I know that sceptre is a type of staff)
'canteen's opening in month before winter sale ends' is the wordplay.
'opening' suggests taking the first letters.
'in' means one lot of letters goes inside another.
'month' becomes 'sept' (Sept is an example).
'before' is a charade indicator (letters next to each other).
'ends' says to take the final letters.
The initial letter of 'canteens' is 'c'.
The last letters of 'winter sale' are 're'.
'c' placed within 'sept' is 'scept'.
'scept'+'re'='SCEPTRE'
(Other definitions for sceptre that I've seen before include "Respect (anag) -- symbol of ruler's authority" , "Royal staff (paired with 2 down)" , "Queen's staff" , "Part of the royal regalia" , "Royal baton" .)