My wife buys "beauty supplies" at a "beauty supply store." She is a beauty -- no air quotes needed. But I'm sure they sell these things other places:
These are really handy for polishing up a knife edge. You have a surface to strop on, and you can get a fine razor edge. Plus you don't have to worry about water or oil and when it stops working you can pitch it. It is nice and light and handy to carry in a Dopp kit or whatever.
If your wife, girlfriend, sister, or roofer, uses these things ask her to save them for you. Or if you happen to be a gay, metrosexual, or merely genderly confused prepper yourself and like pretty nails, we're not here to judge you. I'm just telling you, it's handy for touching up the cake knife as well.