Something like 90% of food in all US restaurants is from Sysco, US Foods, or similar.
Some of them purchase ingredients from those companies, and then make the food using those ingredients.
A great deal of restaurants, though, simply purchase pre-made frozen foods from those distributors, re-heat, and sell it to you at a premium without disclosing while you think it was freshly made. Mac & cheese, stuffed peppers, lasagna, burritos, most 'bar snacks' you can think of, etc.
Some of them purchase ingredients from those companies, and then make the food using those ingredients.
A great deal of restaurants, though, simply purchase pre-made frozen foods from those distributors, re-heat, and sell it to you at a premium without disclosing while you think it was freshly made. Mac & cheese, stuffed peppers, lasagna, burritos, most 'bar snacks' you can think of, etc.