Said ZoĆ« Roberts, a writer and star of 'Operation Mincemeat," quoted in rule #6 — about keeping quiet — in "The 37 Definitive Rules of Going to the Theater/Everything you need to know about seats, coats, eating, drinking, clapping, peeing, compliments, autographs and not being a jerk to those around you" (WaPo)
Rule #6 is "You’ve heard of quiet luxury? Try quiet essentials." We're told you can bring in "water bottles, and even your own candy," but "try emptying candy or snacks into a cup, where you can pluck them out with minimal ruckus."
But Rule #23 creates a big loophole: "Pick your time to sip or bite." It quotes a sound designer who says: "In a musical there are certainly louder scenes where you can probably get away with a little more." Just decide the show is being noisy enough and apparently it's okay to crunch chips.
I feel sorry for the actors on stage. They can see us, the audience. It's not a movie, people. I feel sorry for actors who not only have to tolerate the unreality of a theater full of humans who do not belong in the scene but also have to see us shoveling in food, sucking on straws, chewing, and tipping water bottles up in the air. But the theater people are afraid to call for traditional decorum. They need to fill the seats, and they know we are needy, entitled louts.