Copper, silver, and gold. Who doesn't want them in their pockets?
They say that elements on the periodic table that line up in columns have a chemical kinship. Kinda like notes on the music scale. Each element is like the same note octave above as you down the column (my own analogy, for whatever its worth). The three "coinage metals" are an example of that. Copper, then comes silver, then comes gold.
In chemical properties silver is a super version of copper, and gold is like a super version of silver.
The table is empty at the slot an octave above gold, but they could in theory create a new element that would be in that position in the periodic table that would be a kinda "super gold".
So the three coinage metals are kinda cool that way (on top of them already having a lot of glamour).