Using some cheap Chinese vodka I found (53.7&% APV distilled from sorghum with a little bit of barley and wheat) I started my first three batches of bitters. Aside from the coffee ones, I used Chris Amirault's Hess House Bitters as a starting point. The coffee ones were from the book Bitters but modified somewhat. I have to use gentian as it is the most readily available bittering agent (well, I can get wormwood, but I've yet to see a recipe that uses it as the sole bittering agent).
Coffee, cinnamon and cocoa nibs: self-explanatory. The coffee (I used some nice single origin beans) is supposed to dominate.
Die Boer: I worked off the spices used in boerwors: allspice, coriander seeds, cloves, black peppercorns and nutmeg. Allspice and coriander are meant to be the main players.
Star anise, black cardamom, coriander seeds, Sichuan peppercorns, cinnamon and clove.