We did disney world with DD when she was that age. She had a blast! We brought our own stroller, it was GREAT For the airport and we had lots of connections. When my mom took DD @ 3yo last year though, we only rented and that worked out really great for them. The benefit of your own stroller is that it lays back, we got lots of good naps out of DD @18mo just by lying the seat back and draping a blaket over her.
SNACKS! We packed and entire small rolly suitcase of snacks. Fruit snacks, fruit leather, granola bars, bags of crackers and chips, pretzels, dumdums, etc. We took those into the park and really saved on purchasing treats...i mean you have to do that too, its fun, and part of the trip. But we ate them all by the time the trip was over, then had that suitcase for taking home souveniers. we also bought a case of bottled water and some pop at a grocery store and took that with us into the park too.
There are lots of kid friendly rides. At 18 mos my DD loved the Pooh ride, peter pan, dumbo, small world, and Pirates of the Carribbean. Also look for non-ride attractions like Tom Sawyer and the Swiss Family treehouse (not sure if they have those at land? I've only been to world). Stop and play at the mini park areas that have room for littles to run around, they have a great pooh one in disney and I imagine they have similar. There is also a lot of kid-friendly stuff at Toon Town.
Definitely have hats and sunglasses. SUNSCREEN!! It is SUPER expensive in the park if you forget. Have a small familiar lovey but not THE lovey, since there is a chance it will get tossed out of the stroller. They are nice for napping or tantrum times too. Bring a backpack too, since sometiems LOs get tired of riding and walking, they get a new perspective. Plan on being in the charater shots with them, a lot of kids that age are scared of the costumes. Wet Ones or other disposalbe antibacterial wipes. Great for handwashign on the go and for swiping over an outdoor table. they have the purse packs at walmart and target for a dollar, take a few of them. Nice for refreshing yourself too :)
Remember to go with the flow. LOs that age can get easily overwhelmed, so you made need to take some breaks to just chill. Watch the ducks on the pond, or grab a snowcone and just sit on a bench and people watch. Maybe have a favorite story or two to throw in the stroller for a snuggle time. There's lots of noise and colors and people and that can be a little daunting. Be sure to get a good night's rest for everyone. Don't be too strict about the nutrition, you might drive yourself crazy! I know lots of people don't agree, but I think its okay to let them eat ice cream 3x a day when you are someplace special like that. Get the Micky kids meals and they all come with veggies or fruit. I think they have done a good job on meals. Focus on the FUN and creating the memories. If you don't get it all done, you jsut have an excuse to go back!! :)
Have FUN! I am so jealous, I can't wait to go back! I would go EVERY year if I could afford it!!
Disposable bibs. So nice to keep them clean for pictures and you can just toss them. They fold up so small you dont' even notice carrying them.