OP, you might want to consider using the city airport terminal at co-ex to check-in for your flight in the morning, including your luggage, and do your shopping in the mall. you can take your carry-on luggage around with you, or put it in one of the storage lockers.You can also get your security check with your passport and boarding pass at co-ex, meaning you can use the entry reserved for flightcrew which has a much shorter line. and the limousine bus to icn goes direct from co-ex to the airport without stops in between.