Which should be paired with a long coat or a small bag?

Paired with a small bag.

1. A long coat paired with a small bag highlights the lines of the long coat, making the overall shape more refined, and the small bag is lighter and easier to carry.

2. Pairing a long coat with a large bag can balance the length of the long coat and make the overall look more balanced. Compared with the two, it will be more coordinated with a small bag.