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.