One such fundamental choice is whether to continue to live. It is fundamental because, if decided in the negative, is preclusive of further choices. Choosing not to live can be accomplished either actively (suicide) or passively (self-neglect or self-destruction). These options are worthy of scrutiny, but the fact that most of us never seriously consider them illustrates an influence of human nature on our unfettered choice. Most of us have a strong drive to survive, a fear of pain and death, and a revulsion to suicide. This is a crucial reason why we are here at all to discuss it - self-destructive tendencies are maladaptive.
If we decide to live, then enabling that living must become a foundational element of our purpose, even if we also have further purposes. Procurement of basic survival needs (food and shelter) and management of physical risks are the short-term starting point. Investments such as eating well and exercising, developing positive relationships with others, and improving our minds serve the same purpose with a longer time horizon. Maszlow's hierarchy of needs is a reasonable guide to the pursuit of this purpose.
Only a small fraction of the people in the world have much opportunity to look for purpose beyond survival. Nevertheless, if one does manage to put that foundation in place, it seems that there is another point of unguided choice: "All is well. What do I do now?" Here, a taxonomy of cardinal purposes might be helpful. While not at all definitive, and certainly overlapping, we can organize common aims into the classes of experience, creation, and service. Let us treat each in turn.
Each of us is a conscious agent, and we not only experience the world but can direct both its configuration and our own response to it. Experiences can be pleasurable, interesting, stimulating, exciting, frightening, painful, and many other adjectives. We remember these experiences, and carry them with us. Experience is the most self-focused class of the three, since what it aims toward is purely internal.
Creation expresses something from our mind into the material world; to make physical what starts as mental, and usually (though not always) to produce something persistent and valuable, at least to us and often to others. The scope of creation can be wide, including such products as art, an organization, a scientific result, legislation, or an artifact useful for survival. Creation naturally also involves an experiential component for the creator.
Service aims to generate some value outside of oneself, usually for some other conscious agent, whether other people, a deity, animals, or even a pantheistic natural world. Experience and creation are usually side effects of service, but not the purpose.
It bears repeating that these all overlap, in the ways mentioned and others. A particular purpose often will have components of all three categories. Nevertheless, it is worth considering how each of these categories feeds the impetus for the purpose. This can help with priorities as well as a deeper analysis of motivations. For example, to what extent is one's desire to help others motivated by concern for them versus a desire to feel magnanimous? Is one's desire to play music primarily an act of creation, or is it because we see the joy it gives others?
Finally, we should note that there are questions of temporal and spatial scope that are largely independent of this taxonomy. In creating, how long do we want the creation to last? In serving, how widespread will be the benefits? Experiences have no spatial extent but their temporal extent includes their memory, so one's entire life. Note that larger scopes come with decreasing likelihood of the purpose being achieved. Improving life for all humanity forever may seem worthy, but is also suspect.
One way to make decisions of this kind is resonance. This is an intuitive sense that something feels right, or that we feel our juices flowing while doing or even merely contemplating it. Resonance is not completely irreducible - often we can assign causes from childhood or other experiences that give it this effect; yet the effect is both undeniable and otherwise uncaused. It arises within us without conscious effort.