Hi Julie! It sounds like you are getting ready for a great Fort Wilderness vacation. It is truly one of my favorite places to be and just this past weekend my family was asked which Disney resort they loved the most and the cabins came out on top. You will enjoy the newly refurbished enhancements that were made and I think they are better then ever.
I always tell guests that nothing is impossible at Walt Disney World but you do need to be prepared to open your pocketbook. At the moment I am not aware of any catering service that will come to a private resort room or cabin. The best place to start when inquiring about a private event would be to call the
Disney Floral dream makers. If they can't arrange something themselves they will lead you in the right direction if it is possible.
If the cost for Disney to handle a private affair for you then I suggest you contact one of the local grocery stores. We love the Publix stores when we are at the campground and they can make a meal for you for any number of persons. You will likely have to pick this up and bring back to the cabin yourself. The kitchens in the cabins have a large microwave/convection oven, sink, full refrigerator/freezer, and many baking and cooking utensils for you to use. You will have a dining table that can seat easily 6 persons and you will also have a nice picnic table out on the deck. An outside grill is at each cabin and you can purchase charcoal and other basic food items at the Trading Posts.
Hope this gives you some help in your planning!