My best packing advice would be to put all of the outfits for each day of the trip in separate Ziploc bags. It's so easy to lose little socks and stuff in the suitcase and having to turn it upside down to find one piece is frustrating and messy. Our last trip, I filled a gallon sized bag for each day with:
1 dress
1 pair of leggings
2 pairs of socks
2 pairs of underpants
hair accessory (DD likes her headbands)
(for my 3.5 year old DD)
I put two extra dresses and other incidental clothing pieces (sweat jacket, hat, etc. into a bag as well.
My DD will only wear dresses and skirts

. While this can be frustrating at times, I think I prefer dresses for Disney. It's so easy to throw leggings under them and take them off later in the day vs changing from pants into shorts and making everything match.
In addition to things I already see on the lists, I like to bring:
A sunscreen stick (for touch ups during a day in the park)
disposable changing pads (you never know when they'll be out)
headphones for noise sensitivity
mini look and find books
I always find that I overpack when it comes to entertainment. I'm constantly bringing toys for the hotel when we go on trips and they are seldom touched. DD is always thoroughly entertained by taking a tour of the hotel, visiting the pool, playing with a souvenir doll, or just sitting with a show for a half an hour. I now bring a couple of small things to entertain on the plane because we find plenty to amuse ourselves at our resort.