When Falstaff isn't eating and drinking in this play, he's talking about eating and drinking. Seriously. It seems like he's always on a barstool ordering someone to "Go fetch [him] a quart of sack" with a piece of "toast in it" (3.5.3). The first time we see him in this play he's over at the Page's house getting ready to grub down on some tasty "venison pasty," aka Bambi pot-pie (1.1). At one point, he even says he's afraid a fairy might turn him into a piece of "cheese" (5.5.79).
Wait. That's not all. Even when Falstaff (thinks) he's about to get lucky in the forest with Mistress Ford, he's thinking about food. Check out what he says:
Let the sky rain
potatoes; let it thunder to the tune of Green
Sleeves, hail kissing-comfits and snow eringoes; let
there come a tempest of provocation, I will shelter me here. (5.5.16-19)
Well, the first thing to know is that "kissing-comfits" and "snow eringoes" are types of candy that are considered aphrodisiacs. (Read: food that puts people in the mood for love.)
More importantly, we think this passage says a whole lot about Falstaff's personality. Falstaff talks about food when he's feeling romantic because he's got a huge appetite for everything the world has to offer. In other words, his love of food and drink and sex is emblematic of his zest for life.
At least that's how we see things. The middle-class citizens of Windsor would probably tell you that he's just plain excessive and has no self-control when it comes to food and women. Notice how the housewives are always calling him food related names like "greasy knight" (2.1.94) and "gross watery pumpkin" (3.3.33-34)? That's not just because the guy is big and likes to eat, drink, and sleep around.
For the middle-class citizens of Windsor, Sir John Falstaff embodies everything they think is wrong with the aristocracy—a class of people that's depicted in this play as being lazy, immoral, greedy, over-indulgent, self-centered, and predatory. (Because they kind of were.) Go to "Themes: Society and Class" if you want to know more about this.