Gratitude for results and help is always my preferred offering to any spirit because offering up something physical never made sense to me, as they aren’t physical so they don’t obtain what was offered. I thought about the use of gratitude in interaction with other people, and I would feel helping someone would be a waste in most cases if they did not feel or express gratitude. That got me thinking about why it is like that, and I believe it may be because gratitude is essentially recognition of power, recognizing that someone has helped you and they have the power to.
Perhaps physical offerings are the same in a way that they also recognize that this person or spirit has helped you and they have the power to, and as a way to physically show gratitude and in human relations so that the person who helped also gains something that helps their physical body to survive (in the early days usually livestock, portions of what was gained in a hunt or harvested food were given as payment)
Maybe those who speak with spirits regularly have more insights on this? I know in some cases like with Goetia spirits they enjoy the experience of the physical as offerings, so things like the taste of food, scents etc. can be given as an effective offering.