Fashionable to take a bit of coke? It helps in an emergency (7)
I believe the answer is:
hotline
'it helps in an emergency' is the definition.
(phone line used in an emergency)
'fashionable to take a bit of coke?' is the wordplay.
'fashionable' becomes 'hot' (I've seen this in other clues).
'to take' means one lot of letters go next to another.
'a bit of coke?' becomes 'line' (a line of cocaine).
'hot'+'line'='HOTLINE'
(Other definitions for hotline that I've seen before include "Direct phone link" , "critical link" , "Former direct phone line between the White House and the Kremlin" , "Special phone link" , "Direct telephone link between two officials" .)