Sentence:  An alpine hammer, which has seen better days but never ice, slots into his holster. A wire brush, a nut pick, jumars and etriers all clip onto his harness and his <WSD>butt bag</WSD> (belay seat) goes into his pocket. 
Meaning of the word marked with <WSD> tags:  A seat attached to ropes on which a climber can sit while belaying.