A bottle of water, a torch (flashlight), and a current chart - I cut up the chart - no use including France or Scotland if I'm staying local....and a baby blanket. Gliders don't include heaters.....
And in the back of the Supercub, the operating handbook. Flying with a friend, with the Supercub doors open on a lovely warm day, suddenly the book (which had been forgotten in the back luggage area for years) came apart in the draft! My passenger managed to gather all but three of the pages, we found one on the tail after landing, but the other two were lost forever.