In the few first pages of Walden, Thoreau proposes that there are but four necessaries of life: food, shelter, clothing, and fuel, "for not till we have secured these are we prepared to entertain the true problems of life with freedom and a prospect of success".
I'll call it Thoreau's Pyramid of Needs - food being at the top, shelter in the middle, and clothing and fuel at the bottom. Every part of this pyramid has a single objective: to "keep up the fire within us". Quoting Liebig, he adds: "man's body is a stove [...] the grand necessity, then, for our bodies, is to keep the vital heat in us."
The introduction of Walden states than humankind needs very little to live, and that in fact, most luxuries go against its elevation. Our desires for more food, larger houses, finer clothing, and bigger fires, is the root of all evil. A wise individual should thus strive for more simplicity.
It's the minimalist's manifesto, before it was cool.
Thoreau is not advocating asceticism: he is merely showing the way toward a life with less mundane problems such as growing your career ("I found that, by working about six weeks in a year, I could meet all the expenses of living") or acquiring furniture ("A lady once offered me a mat, but as I had no room to spare within the house, nor time to spare within or without to shake it, I declined it, preferring to wipe my feet on the sod before my door. It is best to avoid the beginnings of evil.").
To Thoreau, esteem, love, a sense of belonging, and safety needs--which are the common needs listed by Abraham Maslow--play very little part in self-actualization. It is rather both an internal and external journey toward decluttering: "to maintain one's self on this earth is not a hardship but a pastime, if we will live simply and wisely; as the pursuits of the simpler nations are still the sports of the more artificial," to which he adds, "I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived. I did not wish to live what was not life, living is so dear; nor did I wish to practise resignation, unless it was quite necessary. I wanted to live deep and suck out all the marrow of life, to live so sturdily and Spartan-like as to put to rout all that was not life".