Saving up for treat on Christmas morning? (8)
I believe the answer is:
stocking
This clue is a double definition.
'saving up for' is the first definition.
'treat on christmas morning?' is the second definition.
(Other definitions for stocking that I've seen before include "Covering for foot or leg" , "Holding for sale" , "Leg wear" , "some legwear" , "Filling up" .)