The next chapter of the book bears the title School Lunches. I read this chapter several times before I figured the point of the essay. It's about taking a subject you're familiar with ane writing everything you can think of that the subject entails. School lunches are something we've all experienced. Whether you ate the lunches provided in the cafeteria or carried a brown bag, you know a lot about school and lunches. But sometimes writing about this for a period of time sends you off on a tangent and suddenly there's an idea for a story or a character in the story you're currently writing.
My take on school lunches changed over time. The ones when I was a nursing student were the ones that really struck home with me and brought a ton of memories. Some of these found themselves into books. Some into books never written. Our lunches were serven in the nursing home cafeteria. Lunch was a half hour. When on duty you had to run across the street or through the tunnels connecting the two buildings. Those tunnels figured a lot in my memories. In the half hour allotted, a run across the street, or down the elevator to the basement, through the dark tunnel and to the elevator to the fifth floor took time. One never had time to sit and enjoy their lunch before they had to run the gauntlet back to whatever floor one was working on.
So doing this kind of exercise is good for a writer. Brings out many things they didn't know they remembered. This kind of memories bring the writer words, emotions and sensations to add to their word. So try the exercise and see what happens when you do. Try it with other times and places from your past and you'll have things to add to your stories.