Have a snack in the theatre (3)
I believe the answer is:
eat
'have a snack' is the definition.
(I've seen this in another clue)
'in the theatre' is the wordplay.
'in' says the answer is hidden in the clue.
'EAT' is hidden within 'theatre'.
(Other definitions for eat that I've seen before include "Make food disappear" , "get stuck in" , "Partake of" , "Have 23d [MEAL]" , "and 27: Be humiliated" .)