I don't think they have much in the way of agriculture. Maybe they plant little plots of squash or something. Mostly they're hunter-gatherers rather than farmers, I guess.

I sort of answered this question in Random Elf Questions Penelope Has. Here are the relevant parts:

Good question. I've waved my hands a bit about what they wear, but I don't think we've ever talked about what they eat.

We do know they must eat meat, since they have bows & arrows (which we assume they did not invent solely to kill each other) and because Lena "sang" rabbits into the pit with Aengus, and because Paul and Osh have been been known to provide the Nothelm kitchens with deer. Also Lar talked once about how his family had to eat his pet goose.

We know they don't eat dairy products of any kind, hence Kiv & Vash's alternating fascination and disgust with cheese and butter. And they don't have alcohol.

So aside from meat that probably leaves fruit and nuts and roots and leaves. Gorilla diet!

However, I think they do have a "cuisine" so they must have recipes and things. Somewhere a while back I mentioned that the ladies who were stuck on "Shalla duty" in the evenings were at least recompensed with sweets or delicacies of some sort.

And of course we've now had the benefit of Vash's Elven Cuisine Lesson One with Kraaia.

I guess it's worth noting that they are living in a valley that was, up until 100 years ago, inhabited and farmed by men. There have been mentions of groves of half-wild apple trees cropping up in the middle of the forest -- the remains of old human orchards. And there may be other types of food that have been self-sowing all this time. So it could be that the modern elves are still reaping small harvests from overgrown old farms and fields. The elven population is a fraction of what the human population once was, so that could probably go on for a time.

Oh, and the khírrón don't eat fish, I think. There is a taboo against going onto open water in boats, so only fishing off the shore would be allowed anyway. And even then fish-eating seems barbaric. Their goddess lives in the big lake, after all.

We know the kisór eat fish, or at least the rebels do, since Dasi's boys complained once about Lar bringing fish for supper again.

They have mostly the same ingredients available, so I am sure the cuisine ends up being similar. Rabbit stew with vegetables is going to be rabbit stew with vegetables, no matter who cooks it.

I don't have the impression that elven cuisine was ever featured much, if at all, at Cat's house. She had cooks to do her cooking, and Paul was determined to live like a man and eat men's food from day 1. Osh and Rua probably went along with that by default. Lena knew nothing about cooking.

On a side note, Cat has never seemed interested in learning about or participating in any elven culture. You never see her hair braided, for example, and she doesn't know the language at all. Maybe it reminds her too much of her trauma.

I assume Egelric ate Sela's cooking, but like I said: rabbit stew is rabbit stew. He probably ended up showing her how to cook some human foods, but I can't imagine Egelric is such a great cook himself. He went straight from his mom's house to living with Elfleda, and he's the gnarliest sort of bachelor when he's alone.

I don't suppose that the kisór have all the same elaborate artifices in their cooking as do the nobles. It's difficult to manage when you're scrounging up what you can to survive. So... rabbit stew.