Herbs, spices, and essential oils can come in real handy. Here's a few off the top of my head that I've used regularly over the years.
Tea Tree Oil
Fennel Seed (fresh seeds or extract)
Oregano Oil (alcohol-free super concentrated works best)
Peppermint Oil
Cayenne Pepper (powder or extract)
Ginger
Cinnamon
Clove Oil
Black Pepper
I also have the
PDR for Herbal Medicines 4th Edition which I highly recommend.