This idea popped into my head years ago after my sons were bickering about who got to hold the giant bucket of popcorn at the movie theatre. I like quiet in the movies and don't want my kids contributing to any distracting annoyances that would bother other theatre goers.
The popcorn costs $7.50, and a trip for me and my sons to see a movie usually costs over $50 between tickets, drinks, and one bucket of popcorn.
I take a plastic (food grade) bag from home to the movies with us. I buy the largest bucket of popcorn. I then move out of the other customer's way and divide the popcorn into bags. The bags are gallon sized so it is easy for me to fill the bags without spilling and making a mess for someone to have to clean up. We each get one bag. Then each person can add salt, or not, and if the theatre has a do-it-yourself butter station, they can add butter, or not. The bag actually works great for distributing it, twist it and then shake it after adding butter and salt. It's better than having butter only on the top kernels in the bucket.
Some theatres have one free refill or unlimited refills with the giant bucket. Sometimes I get right back in line for a second filling of the bucket and repeat. We neve eat more than two bucket's worth.
I like the dividing of the popcorn idea as it stops the bickering. There's no more "You're eating all the ones with the butter" or "I didn't want salt and these are too salty". I also get my own bag to eat slowly rather than feeling I have to grab at what's in the bucket before the kids finish it in ten minutes flat.
We clean up after ourselves at the movies so doing this makes no additional mess for the staff to take care of.
The reason I don't buy my kids the small bag of popcorn each is that the idea of spending $5 on four cups of popcorn and multiplying that by three is ludicrous. It's bad enough that I'm paying $3 or more for bottled water that I pay less than 20 cents for when I purchase it at Costco.