In Soviet Russia, glasses move you!
The very last scene of Tarkovsky’s Stalker has Monkey reading a book while a voiceover (presumably) announces what she is reading, which is a poem. She then closes the book, looks at the three glasses atop the table next to her, then uses telekinesis to move the the glasses. The tallest glass falls off the edge of the table and doesn’t break (very important). “Ode to Joy” from Beethoven’s 9th Symphony plays just as the train starts to roll by, shaking their house/apartment.
The three glasses represent the three Zone travelers (this commenter on the video has a similar idea). The one with the boozy-looking beverage is the Writer, since he had snuck the bottle into the Zone. The one with the broken eggshell is the Professor, representing his abandoned plan to bomb the Room. The tall empty glass is the Stalker, Monkey’s father, and the glass’s falling is indicative of the despair of the situation he expressed to his wife in bed. It could also represent his despair in the Zone after he finally breaks down emotionally and discloses his reasons for being a Stalker, which might be the most emotionally-charged scene in the film, other than his wife’s breakdown in the opening.
The glass doesn’t break after it falls when we expect that it likely should have, indicating that there is still hope for the Stalker’s view on human religious belief and the power of the Zone. This is also directly indicated by the fact that, though there were virtually no visual indicators that the Zone had any power-granting ability at all in the film, Monkey very clearly has some kind of power that’s resulted from the Zone and the Stalker’s involvement with it.