Literally, depending on where you draw a line between luxury and important but not mandatory for most people, it's air conditioning. We have three people in this household that do very poorly once heat and humidity starts to climb, including myself. Plus, uncontrolled humidity in the south ruins things, so there's an increase in costs associated with whatever decrease in power usage would save. For us, AC is right on the edge of being a necessity, as in a medical thing.

But in a more literal luxury that serves only pleasure or want, chocolate. No nutritional necessity, and it isn't like we all can't do without it. But gods damn, it would hurt. A nice piece of good quality dark chocolate is the ultimate mini reward for me. Do something incredibly painful and time consuming, that bit of chocolate is enough to turn it from something that I'm weeping in pain trying to finish into something I'm able to get through before I break down. That's a luxury, but fuck me if it isn't something I lean on heavily as a crutch. I really don't know what I would use to coax myself through really bad days where I'm barely functional but still have to function.