Because most Ferrysburg doors are the post-1980 torsion type, we keep a range of torsion spring wire sizes and winding lengths loaded before we head out, rather than special-ordering once we're on site. That's the difference between a job finished the same visit and one that needs a second trip. We also carry winding bars, a tension gauge, replacement cable and drums, and the safety clamps that keep a wound spring from doing anything unexpected while we work.
What we don't carry is a stock of parts for the older extension-spring, side-mounted hardware you'd find on a house built well before the 1980s. That gear is less common on this side of things, and if we run into it, the right spring may need to be ordered rather than pulled straight off the truck. It's rare here, but worth saying plainly rather than promising a same-visit fix we can't back up.