I think one of the best gruit adjuncts is yarrow. The fresh leaf and flower seem pretty potent as far as enhancing the effects of alcohol. I have a gruit 'wine' going with Danstar Windsor, heather tips, yarrow, bog myrtle and wild rosemary, but it's not quite done yet. Some suggest the effects on this were primarily due to ergot growing on the herbs in their native context, but I am suspecting that while it may be true, the herbs alone do have a nice synergistic effect. Presently I'm making my 'gruit' as kombucha second ferment, and drinking 1/3 bottle of that before having the homebrew definitely does make a big difference. It's an entirely different mindspace ... enjoying it at the moment actually.