allowed at resorts counter service, but only for ice cream desserts -- you can't go back later and pick up bakery item. Some places allow 30 minutes, some allow 60 (we were told 30 min at POFQ, but POP Century said 60 minutes). You have to present your receipt when you go back to get your ice cream and they either mark it with a sharpie, or rip it to show you've picked up your ice cream. I've read they also allow this at water park counter service that have ice cream dessert as an option.
At the park counter service, the dessert options are all pre-packaged items like a chocolate-cake in a cup, or a small bag of apple slices...so you have to take it with you when you get your meal. If you think you won't eat it right then, choose the item that will "travel well" in your bag.