Fortune is the Roman goddess of luck. She was sometimes portrayed as a woman spinning thread at a spinning wheel, and the “wheel of fortune” was a common reflection of how one’s luck cycled between prosperity and disaster. At other times Fortune was portrayed as a prostitute who handed out favors arbitrarily. Here, when Guildenstern says that they are not the button on the top of her cap, he means that they are not overly blessed by Fortune.

 

(Fortuna with the wheel of fortune, found in book by Giovanni Boccaccio, c. 1355-1374)