Offerings are interesting and I admit that I think quite philosophically in this department, going into realms that were not regarded by the ancients.
When one brings it down to the basics what constitutes an offering, what is it?
My point of view is that offerings, sacrifice and devotion is expression.
Sometimes this expression involves objects and physical sacrifice, other times it can be as simple as a breath, spoken word or gesture. But when it comes down to the very foundations of it, it is always an act, an expression. I therefore see offerings as a form of art.
This is one of the core concepts of the Dionysian Artists, (devotional artists). Any act dedicated to the gods is a form of devotional art, thus the devotee giving an offering is an artist. This is a really nuanced philosophy that I go by, but it allows great freedoms of how we engage with the gods. It allows us to respectfully dedicate whatever we can to the gods. The act, by its very nature, is holy.
That aside, the question is about specifics.
Like many aspects of Hellenic polytheism offerings often depend on circumstance. There are everyday offerings typically represent Dionysos in some way like: wine, grains, bread, honey, fruits and flowers, spices, common incense (I prefer pine based oils and Indian style incense.)
Then offerings that may be used during festivals: eggs, meats – especially beef and chicken – resin incense, water, blood (Bloodletting), giving yourself to Dionysos through drunkenness and ecstasy. As mentioned already it depends on the circumstance and intent of the ritual.
Then there are music, art, performance, singing and hymn reading. (Me spending time writing these posts is a form of offering.)
I’m not aware of any general taboos against offerings given to Dionysos.
As a god of foreigners and strangeness I see no problems in offering non-traditional offerings like fruits and veg, spices, incense, modern produce like sweets lollies (candy) etc., not native to Europe or time period. This may be regarded as ‘UPG’, but makes perfect sense to me.
So the skies the limit!