There's always room for discussion, but a simple search for 'popcorn' turns up these previous topics which may answer your inquiry.
How did popcorn become the staple food of the cinemas (and eventually an accompaniment to the home cinematic experience)?
When and why did popcorn become a popular and common movie snack?
When did the eating in cinema appeared? Was popcorn created for this purpoise? Was there anything similar before in theaters?