Packs case of particularly strong drink (7)
I believe the answer is:
scrumpy
'strong drink' is the definition.
(I've seen this before)
'packs case of particularly' is the wordplay.
'packs' becomes 'scrum' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'case of' means to remove the middle letters (outsides of).
'particularly' with its middle taken out is 'py'.
'scrum'+'py'='SCRUMPY'
Can you help me to learn more?
(Other definitions for scrumpy that I've seen before include "Rough strong cider" , "alcohol" , "Strong drink" , "Rough dry cider" , "Strong English cider" .)