Othello includes an embroidered handkerchief that becomes central to the plot in the second act. Performances, such as 1995's film version, include the handkerchief earlier in the film as a part of Desdemona's costume. Shakespeare's plays, as written, do not include prop or costuming instructions, so the necessity to include specific props such as this must be inferred by the director.
How about guns in Chekhov's own plays? In The Seagull, Konstantin Treplyev kills a seagull and brings his rifle on stage. The trope is seemingly subverted when he attempts to use it to suicide and is not successful, but at the end of the play manages to succeed. It is, however, averted in Uncle Vanya, where Uncle Vanya attempts to kill the professor but no clues are given beforehand, and a gun is seen in The Cherry Orchard, but never fired.
Used to great effect in Eugene O'Neill's one act play The Emperor Jones (1920). In the first scene, the eponymous self-proclaimed Emperor explains to another character how he managed to convince all of his subjects that only bullets made of pure silver could hurt him. To demonstrate his arrogance and overconfidence, he pulls out his gun and shows the other character an actual silver bullet he commissioned himself which he keeps inside the gun's bullet chamber at all times as a final resort in case the vengeful natives finally catch up with him. Naturally, the silver bullet is used towards the end of the play, but in an ironic twist, the actual bullet itself is used to 'kill' a terrifying hallucination dredged up by the Emperor's own mind. In the play's final scene, the report of the gun has given away his position to the vengeful natives, who, upon locating their hated despot in the middle of a dark jungle, riddle the Emperor full of homemade silver bullets.
Used in Beaumarchais's The Marriage of Figaro: Marcellina makes a throwaway comment in Act I regarding her long-lost son—who is naturally revealed later to be Figaro, conveniently removing his obligation to marry her.
An actual gun belonging to Joe Keller is introduced in the first act of Arthur Miller's "All My Sons" and reappears in the last scene when Joe shoots himself.
Cyrano de Bergerac: Cyrano’s slight cut at Act II Scene III would be important at Act II Scene VI.
