Sunscreen - apply in the room, and some to carry for reapplication later on.
Wet wipes, hand sanitizer, and a old hand towel cut in half or thirds to dry hands, benches, tables. We would just throw them away at the end of the day. I normally would have a couple of old ones that I would save for the trip.
A change of clothing for each kiddo, if you are going commando, maybe 2 outfits. flip flops for the water rides and fountains. large Ziploc baggie to put them in, work for ponchos as well.
We used a soft sided cooler, that folded up for travel. We would put in juice boxes or Capri suns, we used the gel ice pack thingys. Bring 2 so you can rotate them.
Some OTC med's for grown ups, and little tummies as well. Band-Aids, neo to go.
Snacks, - stay away from things that melt easily.
Something to do while waiting in line, stick with small things - and only use these item while in line so they don't get bored with them.
Glow in the dark necklace and bracelet, pick up at the dollar store. will save you a ton, and maybe you can share with someone else while waiting for the parade to start.
Camera, extra batteries
Extra Ziploc for phones, camera or anything else you don't want to get wet on the water rides. Also wet outfits.
Check the weather sometimes, it will be 80 then drop down into the 50's so be prepared if needed with jackets or sweaters.
Put something on your stroller so you can find it easily, I had this awful scarf that was neon that I tied on the handle made it easier to find. Its funny though I was asked a lot where did I get it at...
Above all bring your inner kid, patience's and have the time of your life.
Have a magical trip
