"MartinM" wrote
Sorry, I'm a caver not a climber, what is a climbing rack? (presumably
nothing like a descending rack)

Collection of carabiners, hexes, stoppers, camming devices, slings, etc.,
carried by a climber to set anchors and place protection while climbing.
Varies from climber to climber and from climb to climb.

As it is perfectly possible to abseil without a specific abseil
device.

again the only thing which springs to mind is an Italian hitch (not
recommended) what other methods are there?

Dulfersitz: Straddle the ropes, bring the rope up and over one's shoulder
from behind, then across the front of the torso and down past the opposite
hip. Painful, not recommended, only works on low angle terrain, only done in
the direst of emergencies. I tried this once on a very short rappel, we were
descending from a long route in Yosemite Valley after bivying on the summit
of Sentinel Rock and my partner thought it would be faster than unpacking
the harnesses. Never again.

Foot brake: Rope is passed under the sole of one foot and over the instep of
the other foot, climber stands very upright and lowers himself with his
hands. I watched a free-soloist do this on the backside of one of the
Boulder Flatirons on my rope after my partner and I had descended. Neither I
or my partner had any interest in trying this novel technique ourselves.

2 carabiner brake: two carabiners laid end to end with enough overlap to
pass the ropes through. Rope is woven through the two overlapping carabiners
as it would be through a descending rack. This is best done with the funny
banana shaped locking carabiners that used to be favored by Czech and other
east European climbers. In fact, I first saw this done by a Czech climber
who proudly told me that this was "East European Technique".

4 carabiner brake: 2 carabiners are stacked on top of one another w/ gates
opposed and reversed. A bight of rope is fed through these carabiners, then
2 more are clipped across the first two to form a brake bar, as in a
descending rack. With enough carabiners, one can build as long a descending
rack as one wishes. Works best w/ oval carabiners. Very effective, very
dependable, every climber should know this technique.
--
mark

BTW I am all in favour of improvising because e.g. incidents on non SRT
trips are exactly where you may have to.