Several thoughts on topics brought up above:
If we struggle with words like natural, necessary, "not necessary," and "empty" to describe desires, we're struggling with Epicurus. Those are his words.
The reason I like "extravagant" is that it's slightly over the top but, for me, evokes Epicurus's own sometimes-playful use of language. The "extravagant" = "not necessary" also evokes the idea of "It's possible to find pleasure in the barest circumstances such as while eating the simplest of meals: barley bread and water, and in the midst of the most dire of straits like at the point of dying in great pain. But it IS nice to have those other pleasures, and we include them all in our definition of the good." That is why I harp on Epicurus, Metrodorus, and Philodemus stating that the internal pleasure of tranquility (ataraxia) is a more secure source of pleasure than pleasure arising from external sources. We always have the pleasure of tranquility readily available in our minds - if we work at achieving it, nurturing it, maintaining it. That's why they place a high value on tranquility.
Stepping back a minute: There are several places where the necessary desires are discussed:
Letter to Menoikeus:
on the one hand, there are the natural desires; on the other, the 'empty, fruitless, or vain ones.' And of the natural ones, on the one hand, are the necessary ones; on the other, the ones which are only natural; then, of the necessary ones: on the one hand, those necessary for eudaimonia; then, those necessary for the freedom from disturbance for the body; then those necessary for life itself. [128] The steady contemplation of these things equips one to know how to decide all choice and rejection for the health of the body and for the tranquility of the mind, that is for our physical and our mental existence, since this is the goal of a blessed life. (My translation)
26The desires that do not bring pain when they go unfulfilled are not necessary; indeed they are easy to reject when they are hard to achieve or when they seem to produce harm. (Saint-Andre)
29Of our desires, some are natural and necessary; others are natural, but not necessary; others, again, are neither natural nor necessary, but are due to groundless opinion.
[Epicurus regards as natural and necessary desires which bring relief from pain, as e.g. drink when we are thirsty ; while by natural and not necessary he means those which merely diversify the pleasure without removing the pain, as e.g. costly viands ; by the neither natural nor necessary he means desires for crowns and the erection of statues in one's honour.--Scholia](Saint-Andre)
Cicero
But how says our philosopher? 'The desires are of three kinds, natural and necessary, natural but not necessary, neither natural nor necessary.' To begin with, this is a clumsy division; it makes three classes when there are really only two. This is not dividing but hacking in pieces. Thinkers trained in the science which Epicurus despised usually put it thus: 'The desires are of two kinds, natural and imaginary;11 natural desires again fall into two subdivisions, necessary and not necessary.' That would have rounded it off properly. It is a fault in division to reckon a species as a genus. 27 Still, do not let us stickle about form. Epicurus despises the niceties of dialectic; his style neglects distinctions; we must humour him in this, provided that his meaning is correct. But for my own part I cannot cordially approve, I merely tolerate, a philosopher who talks of setting bounds to the desires. Is it possible for desire to be kept within bounds? It ought to be destroyed, uprooted altogether. On your principle there is no form of desire whose possessor could not be morally approved. He will be a miser — within limits; an adulterer — in moderation; and a sensualist to correspond. What sort of a philosophy is this, that instead of dealing wickedness its death-blow, is satisfied with moderating our vices?