The druids being one of my keenest interests, I feel I can quite confidently disappoint or at least disabuse you of some factoids there.

While the druids most likely did have some connection to the oak (including through the etymology of their name), all we have to go on for that is Pliny the Elder's Natural History (book 16.95), where he describes the famous mistletoe ritual. This ritual, incidently, seems more concerned with the mistletoe on the robur. Whichever species of oak he thought of by that, for all I know most only rarely have any mistletoe growing on them at all.

Beyond that, we know quite literally nothing about druidic rituals involving oaks, Our sources from antiquity are extremely sparse, and most of our later Irish texts treat druids (draoi) as something pretty damn fanciful from ye olden days, so anything we get from them must be taken with as much salt as you can get your hands on.

Archaeologically, it is almost impossible to identify a burial as belonging to a druid. Other finds, such as sacrificial deposits, for all I know haven't yielded any corroborating evidence on any sort of oak or acorn use for ritualistic purposes or for psychoactive substances (at least not from the Celtic sphere).

I have no knowledge of any use of those ingredients in any sort of ritualistic function, be it from Britain or from greater Gaul. We do not know that the druids used them (Pliny's excursus is on mistletoe, not oak), let alone daily. So your history teacher should read less new-agey nonsense or, much better, provide you with a source other than "I read that somewhere ages ago."

Sorry for the rant, but the very fact that we know so little about Celtic rite and religion makes them the ideal projection ground for all sorts of notions, and this absolutely pets my peeves.