For something to drink, Starbuck's Pumpkin Spice Latte can be found at a number of locations including the Mint Julep Bar in New Orleans Square and the Market House on Main Street.
I tried one but it was way too rich, spiced, creamy, sweet, and pumpkin-y for me (my nephew on the other hand, loved it). At $4.39, it might look a little small, but it has some serious heft to it.
If you're over by the Rivers of America, you can find a not-very-scary Shrimp Po'Boy:
In the nearby Golden Horseshoe Cafe, they have Ice Cream Nachos. Again, not very festive but seasonal.
Speaking of creme anglaise, around this time of year, you can get some freshly-fried Banana Fritters at the the Royal Street Veranda. They're only $3.99 for an order and come with Creme Anglaise for dipping.
On a side note, I asked several employ... er cast members all over the park about their Halloween specials and most of them didn't really have a clue. At one restaurant, they even had an impromptu little meeting but couldn't come up with much (so I hope this is useful to you guys!).