Note: Sorry it took so long. The post kept growing and growing, and my life is chaos. Which, yes, is actually a perpetual state for me. So, on to agriculture and worldbuilding...
There's a lot to know about agriculture, especially in the modern era. It's a science, and even historically it was complicated. Different cultures approach agriculture in different ways, and some are more tied to their products than others, although in a smaller area with less chance of travel, agricultural products tend to form a larger part of a nation's economy. I can't tell you how to grow crops, but I can help you figure out how your culture grows crops, what kinds of crops they're likely to grow, and maybe clarify how that fits into your culture's economy.
The fact that different sorts of crops grow in different climates and locations isn't a surprise to anyone. Once you know what climate your culture/s is living in, you can research similar climates to find out what grows there in our world. Now, you may be making up new plants, fruits, grains, etc. Or, you might be supposing that things we don't (or can't) use as a food source are actually vital to your species or culture. All of that is great. If you want to create a truly unfamiliar or alien world, food is a really good way to communicate that difference. It's a basic necessity, and humans (as your readers are likely to be!) have distinct ideas about what it should be and how it should be eaten. Food is one of the biggies when it comes to the divides between cultures. How we prepare our food, season our food, and what bits we eat/don't eat/are forced to eat can tell your reader a lot about a people.
Remember that in an agriculture system, foods are seasonal. We only have a limited concept of this today because we can import foods from places which are in the grips of different seasons. In addition, our ability to preserve foods (in non-pickling ways) means that we can transport them farther and sometimes have them year-round. This isn't the case in lower tech backgrounds, although in higher tech science fiction backgrounds, it could be even more the case. Perhaps there are whole planets that serve as giant farms: The Bread Baskets of the system.
However, the growing location matters even more when food can only travel a given distance. If your nation is particularly large, there are probably sections of it which have some products while others don't. For instance, anything sea-related is unlikely to travel well, or last long enough to make it too far inland. Someone from the interior of a country is not going to be used to the foods they find on the coast. The same is true of a lot of different crops. Smaller nations may all have access to the same types of food, but you'll also need to consider how far outside of your nation crops and foods can be transported. That will affect which things can be traded with outside regions and which can't be, as well as what types of foods and crops will be found in the surrounding areas.
In addition, there are methods of food preservation which will allow your culture to transport some foods farther, or allow them to keep longer. Food preservation in lower tech backgrounds often meant pickling, smoking, or drying. Grapes become raisins through drying, just as plums become prunes. Dried banana can be really good. Many different types of vegetables can be pickled, from carrots to beets to cabbage to onions and on and on and on. It's important that you do your research because in low tech backgrounds food goes bad quickly. If it's something you wouldn't leave out overnight and still be willing to eat the next day, just think of what it would be like before pasteurization and preservatives.
Spices and seasonings may be common or uncommon in your world; it really depends on the environment in which your culture lives. Herbs and spices can, generally speaking, be fairly easily stored to retain their flavor, so they can be available to a wider audience than items like fruits and vegetables. However, the farther they have to go, the longer it takes, the more risk is involved in transporting them (to both the transporter and the cargo), and the more they cost.
If your culture lives surrounded by nutmeg and mace, than it's readily available, inexpensive, and probably a large part of the flavors of their local foods. Of course, there's every possibility that someone else wanted those flavors and it can reach a point where the people who grow the stuff can't afford to eat it because it's more valuable to them as a source of income.
Also consider the process needed to acquire the spice, crop, etc. There are a lot of ways to get salt (ocean, mining, salt flats), but some are going to produce more than others, some are going to require more hard labor than others, and all these different types of salt are… Well, different. Remember that the price of something depends on a number of things:
• How common is it?
• How many uses does it have?
• How much effort does it take to create/harvest?
• How far does it have to travel?
• How popular/necessary is it?
• Who controls it, and how tightly?
• How often is it available?
Fruits and vegetables are much less portable than herbs and spices. Some can be dried or pickled, such as peppers and plums (prunes). Some travel pretty well, such as potatoes and onions. Some are fairly delicate and aren't going to make it far, such as peaches. Apples are a whole other story because they release ethanol as they age and can actually speed other fruits and vegetables along. Imagine trying to transport those in a closed wagon over long distances!
So consider not only the location in terms of what can grow there, but in terms of what will make it out of there and what won't. Consider the different microclimates and regions of your nations. Foods can become synonymous with the areas from which they come, and you can use crops and foods to help define your cultures and to create boundaries between them.