(I had an ask that got eaten, so)
According to the contents and residues around altars, temples, funerary locations, etc of ancient Greece (studied over and over again in so many locations, and by so many people, both via personal testing and confirmation via primary sources):
the most common offerings to the theoi, nymphs, and heroes were dairy, honey, sweet wine, pomegranates, garlic, grapes, and bread.
So, if anyone is looking to start making offerings, but don’t know where to start: here you go.
Note: fresh, potable water is always acceptable for all gods and spirits and is also very common, but not all theoi will want garlic, as that has cthonic associations (earth, death, underground, etc); the rest is pretty well accepted across he board.
If you’re interested in making more traditional or ancient fare, then recipes abound as well for offerings like spice-mulled wines, honeyed milk, cakes, and flatbreads, bean dishes, fish dishes, etc. It’s all out there, but as a quick primer, here you go.