For off-track calls in a neighborhood built mostly in the early 1960s, the truck carries replacement rollers in both steel and nylon, since older doors here were often hung with steel rollers that have since worn thin - sealed nylon rollers run quieter and don't need the periodic oiling the originals did. We stock straight track sections and the brackets that mount them, because a bent section is more often replaced outright than hammered straight; a track that's been bent once tends to bend again at the same spot.
We also carry cable and drum hardware, since a door that's jumped its track sometimes takes a cable with it, and there's no fixing the track without checking whether the cable's still seated right. What we don't carry on every truck is a full replacement door panel - if the track damage cracked a panel on impact, that's usually a special order, and we'll tell you the lead time honestly instead of promising a same-day fix that isn't realistic.