Wellll, there's not a purported real world thing for either. They were pretty much not wine, mead, beer, or any other human food or beverage.

The kind of thing you're talking about is a fairly modern idea, and isn't exactly backed up by writings of the greeks. They had mead, and they had wines. They had beers. So why would they not directly mention them as such?

The word nectar probably stems from the roots of nek and tar, meaning to overcome death. Ambrosia has a similar etymology from words meaning immortal or undying.

The food of the gods was pretty well established to be something that humans didn't have access to. The myth of Ambrosia the nymph shows that it was never of mortal origin. And the Odyssey specifically compares wine to ambrosia and nectar, which again points to wine not being the same.

Both, however, were definitely liquids. They were drunk, and used to anoint, or even bathe in.

I don't think I've ever seen any translation of any myths of the greeks that indicates that nectar and/or ambrosia were something from the real world at all. Every mention of them distinctly depicts them as being divine and not simply a confused version of human drinks.

Now, if you want to ignore all of that, and guess at what the origins of the myths might have been built from, and you want to ignore the possibility that those myths were completely fabricated rather than being distorted stories of real people (which it's fairly likely that they aren't distorted history), then mead would be a good pick. But, so would entheogens like mushroom teas, or any of the consciousness altering plants extracted.

I would even hazard that, assuming we ignore the same things for this, that a more specific real world substance would be meads made from honeys that are tainted with hallucinogens. We know that "mad honey" was available to the greeks, and that the greeks made use of the kind of plants that bees would access to make "mad honey" in the first place.

The use of entheogens (hallucinatory or not) to connect with or become divine isn't exactly a rare thing. That the greeks may have simply taken it as granted that the gods would have some kind of "magic" food or drink is more likely than them having a distorted history passed down via oral writ.

Ah, ambrosia...

I ate a lot of that. But it didn't make me immortal, it made me fat. (I'm joking of course - the dish above is named after the Greek myth OP talks about.)

Serious now: I think that the myth refers to both honey and mead, without making a distinction between both. I'm saying this because:

• the myth is considerably old, to the point that it has cognates in Zoroastrianism and Hinduism. It's tempting to say that it's an old Indo-European myth, inherited by both sides (Greeks and Indo-Iranians).
• the Proto-Indo-European word *médʰu can refer to both honey and mead (note how it's the ancestor of both English "mead" and Latin "mel" honey). It makes sense if its speakers - i.e. the people who had this myth initially - didn't bother too much distinguishing both things.
• the item in question is sometimes described as food, sometimes as liquid, and it's rather fragrant.

EDIT: about nectar. Both ἀμβροσῐ́ᾱ→ambrosia and νέκτᾰρ→nectar ultimately mean the same thing: "not dying", "immortal" (check the links for etymological info). As such I think that both names initially referred to the same thing, and only evolved into two different mythological food items later on.

I didn't hear about Greek gods consuming amber, only ambrosia and nectar. Translation/language issue perhaps? There is no explanation for what thing ambrosia is as far as I know. I've always imagined it as something that looks like crystalline pumpkin preserve or something, possibly because the word ambrosia does remind me a lot of amber though.

If amber is mead then surely ambrosia is honey