What is a necessity?

That which you need to survive to the point of sexual maturity and create productive offspring.

That means:

• Sufficient nutrition to not die of starvation or become immunocompromised due to lack of micronutrients

• Sufficient water to not die of dehydration

• Sufficient protection from death due to exposure

• Sufficient protection from ionizing radiation to not be render infertile (Earth's atmosphere is enough for most any situation, but thus will allow for different prescriptions off of Earth).

Something that extends your life is not necessarily a need. Humanity went millenia without formal education, internet, or evidence based medicine and didn't go extinct. They are not needs, but valuable luxuries that extend one's life much in the same way a parachute extends the life of a skydiver.

Let me guess, it includes the right to private property, Mr. Enlightened Libertarian?

The negative right to private property, yes; not the positive right.

Negative rights create obligations to inaction. It isn't entitlement.

Positive rights are entitlement;

Is it a luxury to not want to cycle for 30 miles on the 4-inch-wide garbage-littered shoulders, 2 feet away from automobiles going 45mph, whose drivers may or may not be aware of your existence?

They're liable for hitting you whether they're aware or not. Secondly, if there were more people biking you'd probably see better bike paths. Plus there's always the sidewalk.

So yes, it is a luxury.