Drink stuff — stiff stuff! (7)
I believe the answer is:
grogram
'stiff stuff' is the definition.
(type of stiff fabric)
'drink stuff' is the wordplay.
'drink' becomes 'grog' (grog is a kind of drink).
'stuff' becomes 'ram' (ramming is a kind of stuffing).
'grog'+'ram'='GROGRAM'
(Other definitions for grogram that I've seen before include "fabric" , "Coarse material" , "Stuff that!" .)