The Lucky Wishing Coin is a coin and good luck charm owned by Gladstone Gander.
This "lucky wishing coin", as it is called by its owner, Gladstone Gander, is a silver coin with an emblem of a horseshoe on it. Whether it is actually legal tender or a coin made for other purposes is unknown. At any rate, Gladstone once implied that it was the source of his supernatural luck, loaning it to his cousin, Donald Duck, for a day and declaring that without he would be able to "try a normal bit of life."
Behind the scenes
The first and quite possibly only appearance of Gladstone's lucky wishing coin is presumably the 1968 story On Guard, drawn by Tony Strobl, where it grants Donald Duck's wish that the Beagle Boys would attack the Money Bin. While this seems to be the first appearance of the coin itself, the related concept of Gladstone's Luck was invented nearly two decades earlier in Carl Barks's Race to the South Seas.