when I started at McDonald's in 74, Big Mac & Tarter sauce were dairy based products that required refrigeration. By time I left there in 80/81, they were prepackaged with a long shelf life and simply stored in cardboard boxes in the stockroom.
Lettuce and onions were purchased at the local produce store, then shred and diced in 74. Before I left, lettuce was pre-shredded and shipped in plastic bags while onions were dehydrated, simply add water.
Guys before me talked about slicing fresh potatoes to make french fries.
When they started with breakfast, we actually used to crack fresh eggs to make all the egg based meals.
I can't imagine what has changed in the last 35 years