This is a puff piece - just wanted to warn you
I do far more research into fantasy era stuff than any sane human being would do. Even still, I have had a couple of folks challenge me on some of my assumptions and descriptions, so there are folks who are even more far gone than I am.
One of the things I love figuring out is what people in fantasy environments would do with what they have. Let’s take spices. First off, while modern “chefs” dump tons of garlic on everything in order to seem brilliant, I have my fantasy types dumping onions into anything that might be described as savory. But that’s easy.
Lemons and limes don’t grow well in most climates and don’t ship well, so what do you do? Verjuice! Verjuice is (typically) the juice of sour grapes. (I will spare you my sour grapes puns, they were really bad!) In so many ways it was used the way we use lemon juice now a days, sour, easily gotten, typically locally grown. You can use vinegar instead, but that completely changes the flavor. But speaking of vinegar - Fletnern’s cuisines are dependent upon what types of vinegar they use. Wine? Cider? Malt? I normally don’t like vinegar, especially the way it is frequently used in German cooking, but I do love malt vinegar on my beer battered fish.
The other big one I have had to add into my fantasy world is garum. This was a Roman condiment - a kind of fish sauce, typically the fermented guts of fish. Sounds disgusting, right? If so, then why did they use it so much? I’ve never had it, but I have to admit something in my life - I flavor things with anchovies all the time. I know a lot of you just threw up in your mouths a little bit, but I put anchovies in chili (not cooked in it, added afterwards or the flavor overwhelms the whole thing), in tuna salad, in salads, etc. Anchovies - not just for pizza anymore! I think the flavors must be sort of similar - fishy and salty.
So - verjuice, vinegar, and garum - three condiments that were extensively used in ancient times that can be added to your campaign world to toss in some realism and some culture shock. I still believe that if you can get your players talking about the fantasy world as though it were real, you have gotten them to invest in your game, and they’ll keep coming back!