The current legislation of Ukraine does not provide for a single legal act or article that prohibits bringing your own food to the cinema hall. All prohibitions on the presence of own food are established by the cinema itself. But it is important to remember that all the internal rules of the cinema are of a recommendatory nature.
The Law of Ukraine "On Protection of Consumer Rights", namely Part 1 of Art. 17, indicates that the application of direct or indirect restrictions on the rights of consumers is not allowed, except in cases provided for by regulatory legal acts.
If your rights have been violated, you have the right to call the police, go to court and collect moral damages for violation of consumer rights.