One of the Magician's cups is a leather dice shaker.

One of the cups on the Magician's table in the Tarot de Marseille -- the one marked A below -- was originally a dice shaker, probably a leather one.

This emerged suddenly as an unarguable intuition after many hours spent picking over the details of the Magician's table in early Tarot decks. I don't expect my own intuitions to carry much weight with anyone else, though, so here is a bit of circumstantial evidence to back me up:

The cup has a strange square shape -- vertical sides, horizontal bottom -- unlike a normal cup. In the Viéville deck it is unambiguously rectangular in shape, including the mouth. Compare the strangely shaped "cup" in Viéville to the backgammon dice cups and the medieval British dice shaker below.

Leather is brown, a color not included in the standard 8-color palette of the Tarot de Marseille (an exception is the François Héri deck of 1718, which uses it only for the Hermit's habit). What color would be used for leather, then? Well, belts and shoes are normally made of leather, so that should give us a clue. Looking at the 12 decks in Historic Tarots gallery at the Tarot of Marseilles Heritage website, 8 out of 12 use the same color (yellow) for the Magician's belt, shoes, and cup; and each of these individual elements is yellow in 10 out of 12 decks.

Incidentally, this syncs up with the Pythagorean Tarot of John Opsopaus, which, without any pretense of restoring the original TdM, patterns the Magician after the December illustration in the Chronograph of 354 and puts a rectangular purgos, or ancient Greek dice-shaker, on the table. (The picture below is from the original card drawn by Opsopaus himself; the published version, done by another artist, has a round purgos.)