I travel heavy. Especially when driving instead of flying, where I have far fewer constraints on weight and bulk, I have a tendency to try and have backups for everything, usually due to past experiences where I needed it. That includes carrying a spare computer when I'm going to be working from Oregon, besides a clone of the work machine's drive made just before leaving on the trip. So of course on this trip, what should fail on me but one of the few things for which I didn't carry a spare. Due to a tendency to develop blisters on the bottom of my foot (particularly since I've started walking more often), I wear some relatively inexpensive foam rubber metatarsal pads that loop over the middle toe on each foot. They wear out after a few months, so I buy them in medium bulk. But I forgot to toss a spare set into my growing sack of stuff to carry Just In Case. Naturally, it was the toe loop on one of the pads that failed, so the pad will not stay in place. It's not quite annoying enough to justify a rush order to the supplier, but it's a minor hassle.
The way I keep accumulating things to take along makes me sometimes feel like I'm living in the world described in Take a Spare Truss. (It's a pity that none of the sites I searched for this had pictures of the cover or interior illustrations of this highly entertaining book about Victorian travel.)