....In spite of religiously carrying spare spokes in all 3 required lengths I have never in my recollection had to change a spoke at the roadside (except for the first trip away with the newly refurbished tandem in 1981 - changed rear wheel at Camarthen, bought 12 spokes at Waterford, used 6 getting back to the campsite, used the other 6 in 10 miles the following day, pushed tandem back to ferry and train home; the first and last time I have broken spokes on a tandem)....
....re tandem spoke breakage, read low cost, crap wheels in 27" size, too much weight and total inexperience. The replacements broke one spoke in 25 years ( 26" wheels, 12g spokes lf hub brake hubs, trailer for load carrying - so much more fun!)...
sounds like a baptism of spoke breakage fire, that. Some wheels are no-hopers of course; cheap parts that don't fit one another (eg where the spokes are anchored in the hub) or bad quality steel in the spokes, or badly made spokes (eg I have seen some with creases on the inside of the J-bends; these spokes are effectively pre-cracked.....
) . But for average quality wheels on half-decent bikes these days (aluminium hubs, stainless spokes) the single biggest thing is stress-relief in the wheelset.
I learned the hard way (at least 35 years ago now) that 'new wheels' were not 'good wheels' unless they had been stress-relieved; a rash of rear wheel spoke breakages whilst on tour with a load on (in the first few hundred miles on new bought not built wheels) looked like it wasn't going to stop, so when the third or fourth spoke broke in the same wheel, I set to and stress-relieved the wheels thoroughly and hoped for the best. Several thousand miles later I had yet to break a further spoke in that wheelset. [I'd already built several other sets of wheels for myself for other bikes, and they had been OK. I've only used one set of machine-built wheels since then myself and I broke spokes in those too.]
In fact I would go as far as to say that in all the wheels I have newly built since then (including many sets for other people) I have had no spoke breakages. I don't recall handing over a set of wheels without asking that they should be sure to tell me if it ever happens...
cheers