For a snapped or frayed lift cable, the truck carries galvanized aircraft cable in the standard lengths and gauges used on residential sectional doors, plus the drums, S-hooks, and bottom fixture hardware that cable failures usually take out along with it. On a door this age, the drum or the bracket it sits on is sometimes worn enough that swapping the cable alone doesn't fix the underlying play - that gets diagnosed on site, not guessed at over the phone.
Mild coastal temperate conditions here don't put the same stress on cables as extreme cold or heat would, but salt air and humidity still work on galvanized wire over four decades, which is part of why original cables on 1970s doors tend to show wear at the drum end first. If both cables are original, we replace both rather than the one that broke, since the other is on the same clock.