In the movie, Naked (1993), Maggie shows her good luck charm to Johnny and says to him:
Maggie: It’s my good luck charm.
Johnny: Has it brought you much?
Maggie: Has it F*ck.
Johnny: Are you superstitious?
The film is an exercise in exploring unfulfilled promise and bad decisions, including through the mechanism of bleak humour and dystopian imagery. Thewlis's character, for example, is clearly intelligent enough to be, in theory, capable of much more than he achieves.
The good luck charm is approximately a metaphor for the theme of the film. More specifically, the charm and the conversation about it serve to convey to the viewer Maggie's mental confusion, poverty, and poor taste. The "charm" is merely a cheap, mass-produced plastic Troll Doll, a grotesque and pointless artefact of an ultimately impoversishing consumer culture.