Drink scrumpy occasionally with secretary (5)
I believe the answer is:
cuppa
'drink' is the definition.
(cuppa is a kind of drink)
'scrumpy occasionally with secretary' is the wordplay.
'occasionally' means one should take alternating letters.
'with' means one lot of letters go next to another.
'secretary' becomes 'PA' (abbreviation for personal assistant).
The alternate letters of 'scrumpy' are 'cup'.
'cup'+'pa'='CUPPA'
(Other definitions for cuppa that I've seen before include "Drink of tea (informal)" , "Refreshing brew" , "Drink of tea (colloq.)" .)