This isn't meant to be an accurate or comprehensive guide or anything even close. Just sharing some info from my long term personal use, and research of course. Oh, I know it goes without saying but if you're going to ingest anything make sure its quality, food grade extract from a reputable manufacturer. As always YMMV.

Tea Tree Oil - (Antifungal/antibacterial) Use for athletes foot, jock itch, etc. Also a main ingredient in BurnJel® BTW. Make sure to dilute it before applying to skin.

Fennel Seed - (commonly used in the east to help calm the stomach and aid digestion) I grind fresh seeds and make tea or put some extract in a little water and drink it. Tastes like licorice and seems to help with my acid reflux. You'll notice Indian restaurants always serve fennel seeds as an after dinner condiment. And they know a thing or two about spicy foods!

Oregano Oil - (antibacterial/antifungal) Unlike tea tree oil it can be used in concentrated form on the skin without irritation. Of course YMMV. Apparently a lot of research is being done on oregano oil at the moment.

Peppermint Oil - Good for sinus congestion, natural insect repellent, etc.

Ginger - Helps with nausea, settles the stomach, aids digestion, etc. Cut into thin slices and eat raw or add some hot water and make a nice tea. And of course its ubiquitous in asian cuisine.

Clove Oil - Used for toothaches. Its usually included in emergency dental filling kits like the one's sold by Dentek®, and others. Thats actually how I found out about it.

Cayenne Pepper - I've read it was good for keeping intestinal nasties in check and helps prevent colon cancer. Lots of other benefits. Although I'd eat it anyway cause I love hot stuff.