I thought it would be better to start a new thread rather than continue the thread drift from the original question concerning belt buckle tools.

Tjin has a point - "emergency rappel" is a bit of an oxymoron. If you are planning to use a rope, you generally will take along a harness and a rappel/belay device as a minimum, plus whatever other goodies are necessary. However, the need does arise occasionally for an emergency rappel. I have been in situations where it was quicker and simpler to just wrap the rope in a good old dulfersitz and do it rather than fiddle with the harness. Correspondingly, on short, low grade leads it is better to just tie in with a bowline on a coil, do the pitch, and proceed. These situations usually arise on an excursion where there is a lot of hiking and just a bit of technical terrain to deal with.

It is worth knowing that there is a whole spectrum of techniques and associated gear that allows safe use of - 1) just a climbing rope - dulfersitz (body rappel) and bowline on a coil - 2) rope plus nylon sling material and rap device - basically several types of swami seat, -. 3) rope plus harness and appropriate hardware - up to and including the gear suitable for very long rappels and ascents (200 to 1000 feet).

In a way, I am fortunate to have started climbing when the dulfersitz was standard technique. Many climbers today have no experience with this useful, albeit somewhat painful, technique. Back in the day, we would sew leather patches in the right spots.