My whiz-bang item is a pair of folding glasses. I'm practically blind without vision correction, so having a set of spares around is pretty much required. Glasses are an awkward item to fit in a small kit, so I had my prescription installed in a set of optical-quality folding readers. The case is maybe the size of a cellphone. I always take them with me.

The frames are Myspex brand, but I've since found that there are smaller and cheaper options out there. However, my optometrist was impressed at their quality.