Car seat. This one gets controversial if you are staying onsite and won’t need it there, but it was much easier to keep her in her airplane seat when we had her car seat. She was used to her car seat meaning you can’t get up and move around. She airplane seatbelt gives too much wiggle room. We got a cheap Cosco brand airline approved one from Walmart just for travel because they are light and easy to get through the airport.
A toddler sized baby carrier. This is another one that can get eyerolls, but it is a life saver. They make specific toddler sized ones or you can get a standard Tula or Lillebaby that would work unless your 2 year old is especially heavy. You can’t bring your stroller in the lines. It is much easier to toss your 2 year old in a carrier on your back than to try to hold them or wrangle them in line. That changes a bit if your child is on the older side of 2, but we found our almost 3 year old wanted to be held in most lines last year. Save your arms, bring the carrier, but one meant for the size of your child. You will be miserable in one meant for a little baby. I’ve found 2 different carriers at resale/consignment places for under $60 each. Online swap pages are good for them too, and you can resell it after the trip. Bonus, if they are almost asleep and you put them in a front carry position, you can still get on any ride they can do except a horse on the carousel while they nap. Also putting her in the carrier put her at almost my height for the fireworks and I didn’t have to hold her.
Snacks in massive quantities. Easy snack containers to use that close so that birds/squirrels can’t get into them. Or just remember to put them away. We had one of those with the flaps on top where they reach their hand in, but they don’t spill. We came back to the stroller to find a squirrel helping himself. 3-4 sippy cups or straw cups or whatever they like because one will get lost and one will get dropped in the mud.
Cheap glow bracelets from Walmart or the dollar store. We buy them after a holiday when they go on sale because we don’t care what color they are. They are great for keeping them occupied before night shows and good for a tiny light that doesn’t bother anyone if they get nervous in a dark ride. We also put them on their ankles at night to make them easy to find if we let them loose a little bit to play in an area. We buy more than we can possibly use and share to spread the magic.
A rain cover for the stroller. Coming out of a show or attraction to find your stroller got soaked in a pop up Florida storm is not fun.
Some books and small toys for the hotel room. I usually bring new ones they’ve never seen or some I’ve hidden away for a while so they are “new”. This gives them something to do while you get ready in the morning or wind down for the night.
A white noise machine if they normally sleep with one.
Everything you would normally take for a day at the zoo.
I’ll probably come back with more later. If you google Disney World with toddlers there are some bloggers with posts that I found useful before our first trip with toddlers. Some of them are a little overboard, but reading several, I got lots of good ideas and figured out what was frivolous.