Luxury Item - you're crazy
So many post and articles I read are about all the crap you should be taking out of your pack to pursue that ever lighter pack. What is the one Luxury Item you carry in your pack? The item that others would say you're crazy for carrying but it makes you comfortable, happy, or somehow able to justify the weight.
For me it may be a Kilt - When I was bicycle camping I would carry a kilt. Nothing felt better than finishing a hard day's ride and being able to put my kilt on and let everything air out. I am certainly going to consider packing my SportKilt hiking kilt for a hot summer hike.
Depending on how you define "luxury"
I wouldn't consider backpacking without my smartphone. It allows me to keep in daily contact with my wife, to take photos, to know where I am, and to keep up with the world (I learned of the death of a child in our congregation while I was backpacking).
Obviously one can backpack without a smartphone -- or a compass, or a stove, or synthetics, or merino wool, etc. And some people insist, "I intentionally refuse to carry an electronic device, which means my experience on the trail is superior to yours." I simply choose to do so, and would be reluctant to be without it.