Crucial on winter climbs and also potentially useful on rock routes where it can be used to make pocket threads. There are several excellent threaders on the market, but those who which to make their own can do easily with a wire coat hanger. On big winter routes it’s worth carrying more then one threader, as they can be dropped easily, which could prove most unfortunate.
A knife is very important on a descent, both to cut abseil cord, or the rope if it becomes stuck, and often more importantly, cut away all faded and dangerous tat threaded through anchors. Any knife will do, but one with small easily retracted serrated blade with some way of attaching it to your self is best. Take great care when using any sharp object near tensioned ropes as they will slice through them like butter. If you forget a knife then use your axe, a lighter, a sharp edge, or even modify your nut tool so that it has a small serrated section that you can run the cord back and forth on.
Very useful when trying to communicate in bad weather, with the sound travelling a far greater distance then a shout. This should be either attached to the knife with some cord, meaning both items are kept together, or attached to the zipper on your jacket.
Having a set of mechanical ascender on hand can make a huge difference when it comes to overcoming problems on a descent, including dealing with stuck ropes, moving around when finding anchors, and pulling stubborn ropes. Full scale handled ascenders work best, but mini ascenders also work very well indeed, and so it’s advisable for anyone heading onto big routes to take at least one set. Mechanical ascenders do not replace the prusik loop as they can not be easily employed as a back up (unless a single rope is used).