Is there a word to express the idea of everything one could need? I'm trying to figure out if there is a single word that best communicates this idea.
You can consider needs. It can cover all needs including basic, intermediate and advanced needs.
Needs are distinguished from wants because a deficiency would cause a clear negative outcome, such as disfunction or death. Needs can be objective and physical, such as food, or they can be subjective and psychological, such as the need for self-esteem.
On a social level, needs are sometimes controversial. Understanding needs and wants is an issue in the fields of politics, social science, and philosophy.
To most psychologists, need is a psychological feature that arouses an organism to action toward a goal, giving purpose and direction to behavior.
There is the famous Maslow's hierarchy of needs also:
Maslow's hierarchy of needs, represented as a pyramid with the more basic needs at the bottom
The noun necessaries (“Necessary or indispensable items” - wiktionary) comes close to answering the question. An example sentence:
Have you got all the necessaries?
As AE suggested in a comment, one might refer to bare necessities (“Just sufficient resources, with nothing to spare” - dictionary.reference.com) or, quite differently, to a person who has everything, ie has things that go far beyond basic necessities, and typically include luxury items. The sense of necessaries is ambivalent compared to either of those phrases; its interpretation depends on details of cases. For some, necessaries might mean food and shelter, while other individuals might add clothing to the list.
To a person in a so-called "third world country" where the per capita income is perhaps $600 a year, what an average American considers to be a need (e.g., a car) looks more like a greed! And the same goes for an average American with an average income to whom the luxury sports car belonging to a superstar athlete looks more like greed than need. And so it goes.
Granted, the superstar athlete might concede that he could just as easily "make do" with a vehicle which gets him from point A to point B, and so his pricey sports car, he'll admit, is a want and not a need.
Similarly, the third-world person I spoke of in the first paragraph might consider one meal a day, a roof over his head, potable water, and clothes on his back all that he needs. Yet, interestingly, some people who exist at that bare subsistence level will still consider tobacco to be a need, when clearly it is not. Strange.
I think the word you might be looking for, which kind of summarizes what a person feels who has all that he needs, is contentment. To many people--and not just upwardly mobile people, contentment can be quite elusive, however. In a capitalist system, for example, where people feel that hard work and risk taking should be rewarded with all kinds of perks (read: wants, and lots of them), sometimes even "too much is not enough"!
In conclusion, differentiating between basic necessities and wants (or needs and greeds) is a tricky business, except for a person living in grinding poverty. As someone once said, fasting is a luxury for the rich; for the truly poor it is a daily occurrence, and it's called starving!