humans need food, warmth and shelter. anything else is luxury. not bad, but not necessary.
+1 Exactly what I was going to say.
One could strip this down by saying, "anything above what is required to survive is considered a luxury", to be taken subjectively. Now, if an investment banker has dedicated his life to investment banking and is required to wear a suit to work, is that suit a luxury? It could be, because he may have bought an extremely expensive suit above "what is required". Some would still argue that the suit itself is a luxury since he doesn't
need to be an investment banker. It was the profession he chose.
Similarly, someone living in a rural area may have a lengthy commute to work. Is the car then a luxury or a requirement? I would argue that it is both. It is required for its intended purposes. It is a luxury in that it may be above what is actually required (mechanically and aesthetically speaking), or one could argue that it is not necessary to commute to work when one could move and work close to home or really get creative and work at home.
My opinion? The suit and the car in either situation are NOT luxuries IF the job for which they are required is actually REQUIRED (meaning, the job is necessary for survival). They are a byproduct of technological innovation and improvement, and cultural changes and standards (looking formal in a suit). You as a single human being are not going to change these widespread. There are going to be certain requirements for any level of employment that may be considered luxuries should you not need that job or not have a job.
The only trick now is, how do we define survival? Are you optimizing survival by depriving yourself of "luxuries" when you know that by having certain luxuries you will be better off and happier? Why survive when you can thrive? For instance, a computer for myself should be an absolute luxury since I DON'T need it to make money or survive. Yet, I would be extremely unhappy without one. It educates, entertains, and enriches if used for the right purposes. For me, survival is about happiness as well so a computer for me is on the fine line of not being a luxury at all. Now my smartphone? Yes, that is a luxury since I get everything that is "required" out of my laptop.