I frequently brine chicken and pork, and mostly it's just salt and water, sometime sugar, and occasionally garlic.
But I've seen all sorts of other "goodies" people add in, like spices, herbs, sometimes oils, alcohol, acids, fruits, vegetables, etc.
The question is, what actually makes it into the meat? Salt and sugar seem to make sense, and acid or alcohol may affect texture, but I have difficulty imagining that the other brine ingredients are adding any more flavoring than on the outer surface of the meat.
Best Answer
The great benefit of brining is that it opens the fibers of the meat and allows the water, and what is dissolved in the water, into the meat. I suggest you convince yourself of this by adding a fragrant herb such as rosemary to a chicken breast brine, and comparing it side-by-side with an unbrined breast. The difference, deep into the meat, will be noticeable. It is not large chunks of the herbs that find their way into the meat, but the oils and dissolved parts. That is why you heat and steep the water before cooling it for brining.