Radioactivity–it used to be a selling point. Here’s a gallery of glowing goodness (in French, but a lot of the images speak for themselves).
Neatorama likes the Radium chocolate bar. I like the Radium Emanation Bath (pictured), plus a nice jug of “Pure-Radium-Water… Remedy for Rheumatism – Eczema – Stomach Troubles.” That’s right, radium–the proto-Pepto! Of course, it probably tasted better than Pepto. But whatever.