Interestingly enough, food and drinks play quite a significant role. They are key elements of suspense, foreshadowing and plot. The first time we see this is in the very opening paragraph, where Mary has prepared the drinks for her and her husband to have once he gets home. This indicates her love for him, and her total and complete desire to please him. Everything is set out, ready, and waiting, just as she is. Her world revolves around him, and the ready whiskey glasses symbolize that. The next time the drinks are significant is when her husband drains his glass all in one gulp. The narrator indicates that this is "something unusual" for him to do, and if we are paying attention, we can recognize that his drinking of the entire glass and then "going for another one," this time "dark amber with the quantity of whiskey that was in it," is a symtom that something is wrong. The drink is an element of foreshadowing; we know that he isn't himself, and that something bad is going to happen. Mary herself senses it, simply through the way that he drinks. And sure enough, his drinking is just a preface to his betrayal.
Later in the story, food comes in as a key factor. In shock, Mary realizes that she must go cook dinner because they weren't going to go out after all. And, then, the leg of lamb that she grabs is instrumental, as we know, in her husband's demise. Food plays a role again as she goes to the supermarket to play an alibi, and gathers food there for a pretend dinner. Then later, as the cops sit down to eat the lamb, the suspense in increased even further.
I hope that those thoughts helped a bit; good luck!