I am salivating after reading this thread! For me:
1) Dole Float-- MK (DH and I, having not tried one before, decided to share one on our honeymoon. It was gone in moments, and we decided to always get our own henceforth.

)
2) Cherry Danish-- Mara, but probably available everywhere (I don't know why, but I ate one for breakfast one morning and enjoyed it, and I kept getting one the next couple of days. Now I associate cherry danishes with Disney.)
3) Something from bakery in Norway (I don't care what. A bird jumped into my hand and ate coconut while I was there and almost made me die of happiness. All the money we paid, and that moment is my fondest memory of the whole trip. My husband rolls his eyes when I tell him that.

)
The followings aren't must haves, but would be nice to have again at Disney:
3) Filet mignon-- any place that serves it (I had never had filet mignon before Raglan Road, but I don't care for that restaurant too much... I liked it best at California Grill. We were on the dining plan or else I would have never tried such an expensive dish!)
4) Tonga toast-- Poly (Really good, but a little too sweet for me to really crave it again. Also, it was our last day of vacation, so it kind of has a negative association now.)
5) Cheese soup and bread-- Le Cellier (Delicious, though I didn't like my entree or the restaurant in particular.)
Based on this thread, I want to try:
1) Mickey waffles
2) Mickey ice cream bar
3) Popcorn with coke
4) Hot dog from Casey's
5) Strawberry swirl
6) Churros
... and many other things I can't now recall!