How do you keep a toddler busy during a flight so she won't run back and forth to and from the lavatory?

We usually preempt the kiddos before the flight what will our expectations be, how long the flight would be, what are the things they can do or cannot do etc. We tell them where we would be going and use meal times to help them navigate the timing (e.g. after we finished dinner in the plane we will soon reach the beach). We also very much involve them in the packing. I have 2 small bags - 1 is a special treat bag of snacks that they seldom get to eat, like gummy bears; another is an activity bag containing our usual colouring materials and a notepad. So for the treat bag, they get to choose a certain food item (out of my limited 2 or 3 options of course!) to bring along and for the activity bag, they get to choose a certain favourite toy or book for example. They have great memory and will often remember to ask us for the things they chose to bring. And in full service flights, you can also request for children's activities (usually some colouring books or simple toy) or playing cards. Being new, these stuffs usually can occupy the children for quite a while. As my kiddos also like to read, we like to pick up the in-flight magazines to read or simply point out pictures, or just talking about a particular article. When all else fails, we have preloaded favourite movies in our smartphones before flying and that would do as well, although in full service flights the in-flight systems are mostly well loaded with children movies and tv programs! Omitting the in-flight services and items, we practice the above not just on flights, but also on road trips as well. May you have a great flight and holiday! :)