I was also going to suggest the DISabbilities board here on the DIS. They're amazing!!

There's a grea contact to email listed on there. I emailed and received a list of different foods my DS4 (who's allergic to peanuts, shellfish, garlic, trees, grass, weeds, animals, anything else you can think of!) could and could not eat while he was there. They also attached a form to the email for me to fill out and return that listed all of our ressies on it. Since we're going in both Sept and Dec, I was able to put the information for both trips on one form.
On our trip in Feb (1st trip and much less prepared than now), we did not have a problem at all. We always asked and someone came out right away. I remember specifically at Chef Mickey's, they brought him out his own plate of Mickey waffles because they were near something with peanuts on the buffett. He thought this was VERY cool!

The staff did a wonderful job. On our upcoming trips, we're doing custom cakes as we're celebrating birthdays and on both orders they were able to include something for DS4 with the allergies which is great.
Another thing that helps is that I take snacks in our park bag. If I know we're going to pick up a cupcake, cookie or another possible snack he might not be able to have, I've always got something right there that he can have. On the rare occassion he doesn't want it, I give him his options of what's there (usually something like whole fruit or juice) and he's always happy with his choice. He does understand a little bit and will tell people he's allergic. If he sees someone with peanut (like last week when we attended a baseball game and the people in front of us were throwing peanut shells on the ground), he has no fear about approaching them and telling them it will make him sick (he tapped the people in front of us on the shoulder and told them to pick up their mess since the trash doesn't go on the ground and it could make him sick!)

Most people are accomidating (the guy picked up what he could and apologized). If they're not, I will certainly step in and ask that they not take the health of my son in their hands. I also carry his epi-pen and benadryl with me everywhere just in case he gets into anything that someone's touched or anything.
We did not have any problem on our last Disney trip and do not anticipate having one in the future.
HTH a little bit! Have a great trip!!