Need VS want, I could ditch a lot.
I don't need a pair of sunglasses, but I want them.
I don't need a sleeping bag when I pack my coat, but shivering for 6 hours is no fun.
I don't need a camp towel, but it makes a number of jobs easier.
I don't need a spork, but it makes eating a lot less messy.
I don't need a pack liner, but I like dry clothes.
The list goes on....
I think some of my items pass the need/want barrier quite obviously, like the above, but others are definitely luxuries that I do not need to have a good trip. I wouldn't miss my sit pad, but I certainly enjoy it when I do have it.
Then again, I am very masochistic when I camp, so going without something feels like adventure more than sacrifice. For me, the line between luxury and essential is clear.