Drink — rest quaffing another one? (7)
I believe the answer is:
limeade
'drink' is the definition.
(limeade is a kind of drink)
'rest quaffing another one?' is the wordplay.
'rest' becomes 'lie' (lying is a kind of resting).
'quaffing' means one lot of letters goes inside another (to quaff is to drink or consume).
'another one?' becomes 'mead' (I can't explain this - if you can you should give a lot more credence to this answer).
'lie' placed around 'mead' is 'LIMEADE'.
(Other definitions for limeade that I've seen before include "Fruity drink" , "soft drink" , "Citrus drink" , "Non-alcoholic beverage" , "Fizzy drink" .)