In terms of extra cost experiences, we've done the kids cruises out of GF and YC, Pirates and Pals, Wishes Dessert Party with Plaza Viewing, and Wild Africa Trek.
My DS loved the kids cruises when he was younger and the Pirates and Pals cruise was really fun! I really enjoyed the Wishes Dessert Party with Plaza viewing. I thought the desserts were delicious and the viewing area is outstanding. Perfect view and no crowds. Wild Africa Trek was fine, but I was hoping for more "adventurous" experiences like the rope bridge. The food was delicious!