I've been using a Therm-a-Rest chair as linked to in seeker's post above for many years. I have an older one that is even lighter than the 7 oz "Compak" in the current catalog. Just a nylon bag to fit the pad with a few plastic rod stiffeners plus two web straps with buckles. It adds absolutely no bulk to the baggage as it rolls up right with the pad.

I was stranded in Tropical Storm Andrea for 24 hours two summers ago. Was able to sit up comfortably in the tent and read. It's useful at campgrounds in Europe where picnic tables are often not supplied. Also handy for lawn seating at outdoor concerts. It utilizes the pad you're already carrying. You don't need a tree for support as in Machka's photo.