We ate at Flame tree last sunday. Tried to sub fries for dessert and onion rings for drink. They said no, you can only substitute one or the other. So we ordered the onion rings and a drink. Then while waiting for our food, they gave us fries instead- We said no, we ordered onion rings, as was on the receipt. It took them so long to figure it out and get us the onion rings they said just keep the fries. So it kind of worked out, except the fries were cold by then.
We also substituted at:
Pecos Bill: Drink for a side of Chili
Pepper Market @ Coronado Springs: drink and dessert for a side of mac and cheese and a side salad
Katsura Grill: Edamame instead of dessert (wanted the iced green tea, so didn't ask about subbing)
Tangerine Cafe: Side of cous cous salad instead of drink (wanted the baklava dessert, so didn't ask about subbing)
For Sit down meals, we didn't try substituting dessert for a side since we only did one non-buffet/family style- and we wanted the dessert and Tutto Italia!
I hope this helps someone!