What is the one thing you MUST do or your Disney trip is not complete? I'm not talking major headliner attraction. Just something you or your family always make sure you do every trip. Whether it is a particular unpopular attraction, a special snack, character meet, etc. For example, we have a few:
Carousel of Progress - nobody loves it, but it would be weird if we skipped it!
Funnel Cake for breakfast from the little place next to the castle.
Muppet Vision 3D
Soda tasting at Club Cool

Curious to hear what other small thing is a CAN'T MISS for others.