I've been pretty lucky, only one significant gear-fail I can think of, but it was painful: On a Rainier mini-expedition/climb in 2006, on the way out after a fantastic climb on the Emmons glacier route, heading down my waist belt buckle broke. We were loaded with all sorts of technical gear hence very heavy, plus we had leftover food & fuel because we summited on our first of three summit days. Probably a 55 pound pack, no waist belt, a 6500 foot descent on steep snow then rock then dirt. Painful! I tried all sorts of jury-rigs, never managed to get it tight enough to take the weight off the shoulders.

Ever since then I always carry a spare waist belt buckle. My ULA OHM buckle "broke" (stopped snapping closed) on my AT hike, used the spare then, very handy!