Long bag containing sugar, perhaps unwrapped (4)
I believe the answer is:
ache
'long bag' is the definition.
'ache' can be an answer for 'long' (to long for something is to ache for it). I am not sure about the 'bag' bit.
'sugar perhaps unwrapped' is the wordplay.
'sugar' becomes 'ach' (I can't justify this - if you can you should give a lot more credence to this answer).
'perhaps' becomes 'depends' (I've seen this in another clue).
'unwrapped' means to look at the middle letters (the letters which wrap the word are removed).
The middle of 'depends' is 'e'.
'ach'+'e'='ACHE'
'containing' acts as a link.
Can you help me to learn more?
(Other definitions for ache that I've seen before include "Dull throbbing pain" , "Similar" , "Dull steady pain" , "Shakespearean character" , "anguish" .)