One of you got a letter that was meant for the other and is delivering it to the proper recipeint. (Is it open? Does the envelope/parcel give anything away about the characters? is the parcel in good condition?)

One of you spies the other using an effective and largely unknown technique. (Special kind of fabric stitch, attack style, magic, hunting technique, etc)

Party A is new to the area. As a person approaches them to offer a good or service, Party B overhears and knows them as a charlatan.

One of you is traveling from one town to another by a chartered carriage that has had a wheel break. The other comes along on horse back as the carriage is undergoing repairs.

One of you has just unkowingly committed a cultural faux pax (hand gesture, turn of phrase, table manner, handling of an object) and the other educates them on the custom (quietly and in secret? Loudly in front of others who may not have even witnessed it?)

Party A was told a personal story by a traveler and shares it with Party B. The story is remarkably (or exactly) simiilar to an actual event that happened to Party B.

One of you has found an object that is not whole (book missing pages, part of a piece of jewelry, etc). While talking about it, the other over hears and presents a missing piece, but the object is still not whole.