Chicken strips are from the Children's Menu in restaurants, the Room Service Menu, and they have recently been restored to the menu at Pluto's Dog House, on deck 9 by the pools (thanks
DCL!).
I don't know about doughnuts, maybe they're in the Buffet restaurant on deck 9 for breakfast, we rarely go there. I can speak for the croissants and muffins that are served on the Room Service menu at Breakfast. They are very good. I think I've seen the same items on a tray in the full service restaurants for Breakfast. They have fruit flavored muffins like blueberry, some bran muffins, and a chocolate chip muffin that is really good. It was a muffin with tiny chocolate chips here and there, it wasn't overly done with chips, just a tasty little prize here and there. The croissants are light and fluffy on the inside.
The pizza slices are good at Pinnochio's on deck 9. The pepperoni and cheese and the cheese pizzas are thick and gooey when warm. They are not made up that far in advance, at least late in the evening when I had some. They tasted very good and it was warm, I had to wait a couple of minutes until they were finished. We never had more than two slices at a time and ate them on deck 9, so not sure how they would be later in your cabin.
On the 7 night cruise, they had a Mexican Buffet for lunch at Topsiders. Among other items, they had a Mexican Pizza that was very good. I would have taken less of the other food if I would have known how good it was.
They have an appetizer at Palo's that is a pizza. I was reluctant to order it because I didn't want to eat that much, I was looking forward to the entree. Our waiter talked me into it and I reluctantly agreed, warning him I would not finish most of it. It was wonderful. It was a very thin and crispy crust and it was more personal sized than I had anticipated. It was so good that I regret insisiting that my DW taste it. The waiter was very tactful when he cleared the appetizer plates and said something like 'oh you finish it, you must have liked?'.
They have an appetizer in the dining rooms called 'Duck and Goat Cheese Pizza'. It was under my heading of 'things I wouldn't order at home' so I tried it. It was different, it was small, and it was 'interesting'. You should try it one night when it's offered.
We haven't ordered a pizza from Room Service, maybe on the next cruise?
hope that helps