I was on some jam packed thruway or other taking the great aunt (early 90's, mostly housebound and excited to be in a car out of her apt.) of a friend's son to a dance performance north of NYC and the spring broke - engine raced, fortunately in bumper to bumper traffic. The first time right there in traffic on the thruway,(repair was short lived) I was able to bend the remaining hardened steel into a 'new' loop. Got off the thruway and, somehow it came unhooked and fell off. After much searching I ended up making a temporary 'spring' out of a paper-clip and an elastic hair scrunchy my wife donated. After the performance (at a college) we went to the sculpture dept. and I wound a piece of 1/16" welding rod into a better spring.
Not a failure I would have thought to prepare for, but I'd carry a spare now, if I remember.