First of all congratulations!!!
I've been twice with 10 month olds, both my oldest dd and my youngest dd went at that age. It can be very fun if you are prepared! I learned a few things after the first trip so I'll give you all my suggestions even though some will be repeats of what other posters said.
Have a stroller that is easy to fold quickly, lays flat so baby can nap in it, has a good sunshade, and bring a rain cover for it. If there is even one single cloud in the sky, cover the stroller anytime you park it and most especially if you are going to be gone awhile for eating or a show. Really sucks to come back to a soaking wet stroller and soaking wet diaper bag.
Take 2 extra changes of clothes for baby in addition to the diapers and wipes, snacks, and formula if you are bottle feeding. Try to use just one bag to carry all that in that is one giant open pocket without a lot of extra little pockets, this will make going through security much faster and easier. Buy clips for the bag if needed but make sure it goes on and off the stroller quickly and easily, both for the security line and for getting on and off busses.
Here are some after market things I bought for my stroller:
http://www.amazon.com/Summer-Infant...=1425136496&sr=8-1&keywords=stroller+sunshade
http://www.amazon.com/Stroller-Hook...qid=1425136542&sr=8-3&keywords=stroller+clips
To make carrying things easier, I left only clothes and diapers in the diaper bag and left that on the stroller at all times except loading and unloading from busses. I left nothing expensive in it. I carried a small crossbody bag for my camera, phone, wallet, and also one extra diaper, disposable changing pad and wipes, and one bottle of formula. My biggest fear was getting stuck on a ride like Pirates for an hour or something with a screaming baby who was starving. Or coming back to a stolen diaper bag and having no more diapers or anything with me.
Here is what I used for feeding to make life easier on the trip:
http://www.amazon.com/Similac-Advan...id=1425136759&sr=8-9&keywords=similac+formula You can get these cheaper at a local store than online. These can be carried and fed at room temperature, which makes them perfect for traveling. Then I used these and just threw the whole thing away afterwards
http://www.amazon.com/25-Enfamil-St...1425136913&sr=8-1&keywords=disposable+nipples
With my second dd I used a sling carrier for carrying the baby in lines after not having one the first trip and it was a godsend! Here is the one I used:
http://www.amazon.com/Balboa-Baby-S...qid=1425136141&sr=8-1&keywords=dr+sears+sling It was perfect imo for Disney because it allowed me to carry the baby on my hip in a natural position where she could lay her head on me and nap as needed, but when we sat down on the ride I could easily slip it over her head and then sit her on my lap to face forward so she could see. Then when the ride was over I could easily put her back on my hip and slip the sling back into place without holding up the exiting people behind me. I swear this thing saved my arms from falling off. It also wasn't too bulky so I could just keep it on when the baby wasn't in it during the rides. Whatever you choose make sure it is easy to put baby in and out and take on and off cause you will be doing it frequently
My other advice is to just try to keep the baby to their schedule as much as possible. From 8 months to 10 months the schedule won't change that much so you will have a good idea of when nap times are before you have to do FP+. Don't schedule M&G during nap times and expect cute pictures!