We used table service credits for room service on our recent stay at AKL. When you order room service tell them at the beginning you're on the dining plan, that way the cm know's what you're entitled to. For example at AKL I wanted a milkshake as a drink, but I was told that would count as my dessert.
When they bring the order, just sign the receipt which will tell you how many credits you have left, same as in any table service restaurants. Although it probably wasn't the best use of two credits, we got a lot of food and the food was tasty.