As with phonology, paying just a little bit of attention to the food your characters eat can go a long way toward making your invented world feel real and lived-in and coherent.
Let’s start with something basic: what’s the staple grain? Just taking a moment to specify whether it’s wheat, millet, oats, barley, rye, rice, maize, amaranth, or quinoa pops the world briefly into three dimensions. What fruits are available? If it’s a temperate climate, things like pineapples, mangos, and guava will be out of place. If your characters are tramping around a jungle, having them stumble across blueberries or pears would be implausible. If the people keep livestock, what kind? Chickens have proved capable of thriving damn near anywhere; so have pigs, though they’re more likely than chickens to be the subjects of dietary taboos. Other creatures need a lot more pasturage or are pickier about their environmental tolerances. For cows to work, there needs to be quite a lot of grass available; in dry climates you’ll do better with goats or camels.
There are a great many edible plants and animals that we tend not to think about today because they aren’t amenable to modern industrial production, or have been replaced by alternatives that are tastier or more nutritious or easier to prepare. This seems to be especially true of fowl: these days I only occasionally see duck in a non-Chinese restaurant, but Europeans used to regularly consume duck, pigeon, swan, grouse, and more. Ditto for other small animals, like rabbits — or in other parts of the world, dogs and cats, and horses on the larger end of things.
And even if it’s something we still eat today, don’t assume that its cultural role has always been the same. For centuries oysters were a cheap London street food, before the pollution of the Thames drove stocks into a decline. Lobster was despised as fit only for the poor; in the U.S. they regularly served it to prison inmates, which is unthinkable today. (There is apparently no historical evidence for the common assertion that servants’ contracts specified they would not have to eat lobster more than twice a week.)
What about the form the food takes? Some things are essentially universal, like soups and stews, or the art of wrapping something edible in something else edible — whether you call the latter a taco, a spring roll, or a dürüm. People around the world have always experimented with fermenting anything they can, from rice to grapes to milk to sharks. Other types of food are not necessarily as widespread as you might think, like leavened bread. We sometimes talk about the role of estrangement in speculative fiction — causing the reader to see a familiar thing in a new light — and this is an easy place to do that; have a traveling character recoil when offered lumps of curdled milk, aka cheese. (I had fun with this one in the Memoirs of Lady Trent, where the protagonist is raised in a Judaism-based religion and is horrified to discover that while ill in a foreign country, she was fed a broth with “pig meat” in it. If you don’t consider pigs to be food, you aren’t going to have the word “pork” in your vocabulary.)
That leads us to the question of imported foods, which can also add a lot of color to the story. What kinds of things do they have the capability of importing, and what is considered worth the effort?
It’s easy to forget nowadays, with many grocery stores stocking produce from all around the world, but in the days before refrigeration and fast long-distance travel, the food available in any given place would often be pretty limited, and imports could be ludicrously expensive. Historically spices have been a tremendously desirable cargo because their value-to-volume ratio is high, and they keep well enough to survive a lengthy journey — and when I say “spices,” I don’t just mean the ones that are still expensive today (like saffron), but things we now consider to be utterly ordinary, like salt and black pepper. I’m told that the very first edition of Julia Child’s cookbook introduced the average American reader to an exotic herb called thyme and explained how to get your local grocer to order it in — thyme! One of the least unusual things in my spice cabinet! But fifty years ago, things were different.
Other foodstuffs don’t travel so well. In the trailer for the movie Victoria and Abdul, Queen Victoria’s manservant Abdul Karim tells her about the fruit of his native India, which leads her to demand that a mango be shipped to England. Even with Victorian innovations to help, when it arrives it is . . . an ex-mango. Some things could be packed in ice, but prior to refrigeration technology ice was only available in some seasons and some locales, which were often not the places producing exotic fruits.
The better solution was to try and transplant the exotics directly. If you wanted oranges in Renaissance England, you could import them from Spain, or you could build a greenhouse and grow your own. They might not be as good, thanks to the different climate, but they’d be a lot cheaper. In the nineteenth century Britain went to great lengths to smuggle tea plants out of China so they could break the monopoly on that trade by growing their own supply in India. Animals pose more of a problem; importing enough living specimens to start a breeding population is difficult, especially since some animals travel even less well alive than they do dead and unrefrigerated.
November is a very appropriate time to bring up the Columbian Exchange, i.e the massive transfer of species between the Old World and the New. It’s no accident that the Thanksgiving menu often features things like turkey, potato, pumpkin, corn, cranberry, and sweet potato, all of which are indigenous to the New World.
Some readers will get kicked out of the story if you cross your culinary streams, e.g. by having tomatoes in the very European-feeling setting of The Lord of the Rings. (Italian food without tomatoes! It seems unthinkable . . . but that really only became a thing in the nineteenth century.) Me, I don’t mind it; as long as the climate is appropriate, there’s no reason you couldn’t find plants and animals from different parts of the real world occupying the same region of an invented world, even before they have the trade necessary to introduce lots of invasive species.
But if you’re worried about that kind of thing, just do a bit of research into the food that was eaten in a given place and time comparable to the society you’re writing about. Then your characters can eat fufu or nattō instead of generic stew or roast beast, and your world will seem just a little bit more real.