For calls out this way we carry what actually fails on 1980s-and-90s chain-drive openers: drive gears and sprockets sized for the common residential models from that era, replacement chain and rail sections, run capacitors, and travel-limit switches. Photo-eye safety sensor kits go on the truck too, since a lot of original installs from that build window predate them being standard equipment on the door.
What we don't carry is a shelf of discontinued circuit boards. If the logic board itself is dead on an opener that old, the honest fix is usually a full head-unit replacement rather than hunting for a board that hasn't been manufactured in twenty years. We'll tell you that straight rather than string out a repair that won't hold past the next power surge.