The trick to the author's math is this:

A loaf of bread has, say, 24 slices in it. If you ate two of them, then the cost of bread was that day $0.34, when you amortize the loaf of bread over twelve days. If you can find a $2 loaf of bread with 24 slices, it's only about $0.08 for a slice of bread.

But yes, I agree -- if you actually had to maintain this budget, you'd probably buy one kind of breakfast, lunch, and dinner and eat it every day for a week.