I'm allergic to dairy, beef, and eggs. Disney is simply the best for food allergies!
At the Main Street Ice Cream parlor you can get a nondairy "ice cream". Its delicious. Just tell them, they will call a manager over to do it and sign off on it. Its really nice to have that reassurance.
As for other snacks-frozen coke or whatever other flavors they have, blueberry or cherry is always good. Frozen fruit bars, any fruit, chips, I personally LOVE pickles! They also carry Divvy products
http://www.divvies.com at a lot of locations which you can ask for! YUM!!
Counter Services are just as easy to navigate. Here are my favorite by park:
MK-Cosmic Rays: has tons of options!
EP-Sunshine Season and just about any country
HS-Pizza Planet-great salads
AK-Flametree BBQ
First and Foremost Do not be afraid to ask questions! Any CM or Manager will be happy to accommodate you! Last thing they want is you getting sick!