When taking the limousine bus to Seoul, be careful not to lose the baggage claim ticket you receive when boarding.
If staying in the Yongsan area, be aware that you might not be able to charge your climate companion card at Yongsan Station; Sinyongsan Station is where you can charge it.
The Hyundai I'Park Mall is large, so it's recommended to check which stores you want to visit beforehand.
When buying food items, check international flight rules.