This quote comes from a conversation early on in the play when Charley and Willy are talking about Biff and his future prospects. Charley makes an analogy between Willy's plans for Biff and a "deposit bottle" in order to try and get Willy to accept that his glorious plans for Biff are not going to materialise into anything substantial. Note the context of the conversation, and what Willy says that leads to this comment being made:
I can't understand it. He's going back to Texas again. What the hell is that?
Willy is expressing his complete lack of understanding about Biff choosing to head West again and work once more on a farm. Charley's analogy is therefore meant to stop Willy worrying by comparing the dreams Willy has of Biff's "making it big" in the city with a deposit bottle that is broken and cannot be redeemed. In essence, Charley is telling Willy to forget about his dreams for Biff and accept that Biff has chosen a very different way of life compared to the kind of life his father wants for him. This is of course something that Willy is unable to do, as that would mean he would have to confront the truth about the failure of his own life and career.