Figure of Eights and other kit for rapid descents (but not too rapid!).
Many climbers these days no longer carry a Figure of Eight for abseiling as the majority of Belay Devices can be used instead. Moreover it has been shown recently that Figure of Eights can, in certain situations, twist against the gate of a Screwgate Karabiner and break it open. This has resulted in several deaths. For more information see Neville Macmillan's paper Karabiner Breakings when Using a Figure-of-Eight.
However a Figure of Eight is useful in many instances and remains the first choice for those who abseil regularly due to its larger surface area and greater heat dissipation. The problem of accidental gate opening can be counteracted by using a special Belay Karabiner. A good way of backing up an abseil device is with a Prusik Loop or a Shunt.
Although Figure of Eights are sometimes used for belaying, the friction is not very high, and we do not recommend this.