Units are given a budget to spend on food for the troops. Lobster, King Crab, and ribeye steak were prepared about once a month, or when returning from a long training exercise. They were too expensive to have around all the time. Our cooks made donuts every day; they were not purchased in bulk. They were all made from scratch.
As a young recruit, I did my share of KP duty, and one of the nastiest jobs they gave us was cleaning grease traps. The oil used in the deep fryers for donuts in the morning had to be emptied. Then fresh oil was put in for French fries and/or fish cakes for lunch or dinner.