Dropping off mail at the post office or picking up a prescription

ERRAND

Think of a quick task you might do on your way home, like returning a library book or grabbing groceries for one item.

This clue describes a common task like delivering mail or grabbing medicine—both examples of quick, routine trips you’d make outside the house. The word "errand" fits because it’s the general term for these small, practical outings that don’t take much time. There’s no wordplay here; it’s a straightforward definition pointing to a simple, everyday activity.