Just did a 1 day trip to the Magic Kingdom last month. I used mainly my 30mm 1.4 and kit 18-55mm on my Canon T2i.
Here's what I liked/didn't/what I would do differently.
The 30mm was great for indoor events where you meet characters, like the Princesses and Mickey Mouse. Lighting is pretty dim in there. Also, the lighting is often weird and colored, so shoot RAW so you can play with white balance later. I did not bring my flash, because I assumed I would not be able to use it. Big mistake! Really wish I had brought it. All of the Disney photogs use flash indoors, and often outdoors too for fill. No problem using flash at most places. If you have a good flash (not the onboard one) you will get better results, faster focusing (at least with my canon and the focus assist beam), etc. That being said, I was able to make the 30mm 1.4 work for most things. A few shots could have used higher shutter speeds, but didn't have a lot of time to play with settings.
Now, for outdoors the 30mm is also decent. But, there are times where I wished it was wider, or had more zoom. Often I was able to crop in on something, so that helps the zoom end of things. Most times I would flip to my 18-55 outdoors.
So, if I had to do it over again, I would definitely bring my flash. But, one of my biggest priorities was getting good shots of my daughter meeting the princesses, (mission accomplished!). Your focus could be different.
If was going to bring just one setup, I would seriously consider the 18-55 plus flash. Or, maybe rent something like a 17-40 or 24-105 f/4. If not bringing flash, then the 30mm for sure, because a slower lens ain't gonna cut it indoors.
I had a camera backpack on the whole time, so lugging stuff was not much of an issue. But, you also don't want to be swapping out lenses constantly. so a versatile kit is nice, which a zoom plus flash gives you. Also, there are lockers in most parks so you can store stuff you don't need the whole time. Like, if you want a tripod for at night or a different night lens, put it in a locker.
Also, here's another tip: The photopass people there that take your picture at the various events will be more than happy to take your picture using your camera. Just dial in your settings before handing it over, as they won't usually adjust aperture or shutter speed. But, they are pretty good at handling the camera and doing a decent composition. So, if you want to be in some pictures, just ask them to take a few!