My preschooler has sensory processing issues, and as a result is the most antsy and wiggly child I have ever seen. So any type of waiting results in issues if we are not ahead of the game.
Other than food (since eventually most kids will stop eating when full!) we have found a variety of "busy bags" to be really helpful. We have also used these for other kids and cousins on different trips, airplane rides, etc. (I'm the mom that will throw your kid a busy bag to share in line

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Things with a lot of small parts don't work well, but you can have some pieces since they are all in bags.
Pipe cleaners and foam beads - these are LARGE foam beads, like as big as my eyeball. My son makes bracelets or necklaces, or we practice patterns. The beads are large enough that he doesn't drop them often and when he does they are easy to see and grab.
Rubic's Cube or similar hand puzzles. We have found a lot of things in the dollar section of target or the dollar store.
Stickers. We have rules - stickers on clothes or the stroller, okay. Stickers on walls, not okay.
Small figurines/stuffed toys. We have a couple travelers that go with us most places, one is a small Mickey. We act out scenes or I ask him to show Mickey what he sees in line/out the window/etc.
For other places you have to wait (there is a LOT of waiting in this world, isn't there?) like waiting on food or waiting on a parade, you can use bags with more pieces. We have a bag that has a princess figure with the snap on clothing. A busy pack that has a coloring book, stickers, and crayons (I find them at the dollar store or target, they are in little mylar type bags). Small party-size jars of playdough. Felt play sets (making sandwiches, cupcake decorating, etc).
Just do a search on Pinterest for "busy bags"!
