My favorites are:
1. Spicy Cheese Pretzel @Auntie Gravity's in Tomorrowland (I get several every trip!)
2. Dole Whip Float (of course!)
3. I always get some sort of Fudge at the Main Street Bakery... the Pink Lemonade Fudge was yummy I like to see what new ones they come up with
I agree with the PP - Dole whip Float (not just a dole whip, which is just the ice cream) - Available at Aloha Isle in Adventureland
Figaro Fries for a more salty/snacky treat - Available at Pinocchio's Village Haus in Fantasyland
Homemade Mickey Mouse Rice Crispy treats with the ears dipped in chocolate - Available at Main St Bakery on Main St.
Also, just a quick stop at the Main St Confectionery is a good bet for finding a delicious treat!