I made it [bread] according to the recipe which Marcus Porcius Cato gave about two centuries before Christ. "Panem depsticium sic facito. Manus mortariumque bene lavato. Farinam in mortarium indito, aquae paulatim addito, subigitoque pulchre. Ubi bene subegeris, defingito, coquitoque sub testu." Which I take to mean, -- "Make kneaded bread thus. Wash your hands and trough well. Put the meal into the trough, add water gradually, and knead it thoroughly. When you have kneaded it well, mould it, and bake it under a cover," that is, in a baking kettle. 

The third thing that must have been of the greatest importance to Thoreau was books. He graduated from Harvard, and could have taken a master's degree; but he was not like some students who think their education has come to an end when they turn in their caps and gowns and sell all those heavy textbooks. He continued to read serious literature for the rest of his life.

Books are the treasured wealth of the world and the fit inheritance of generations and nations. 

Another thing that was of great importance to Thoreau was his writing. He wrote millions of words, and his published writings fill twenty volumes. But writing is a form of thinking, so his writing might be considered a part of his philosophy. It would seem that the three things of greatest importance to Thoreau, then, were philosophy, nature (the love of nature and the study of nature), and freedom. Truth, of course, is an essential part of philosophy, as are reading and writing. He chose to lead an extremely simple life because he did not want to waste precious time earning money. He says in Walden:

"But I have since learned that trade curses everything it handles; and though you trade in messages from heaven, the whole curse of trade attaches to the business.”