Myeongdong has Daiso Myeongdong Main Store (43 Myeongdong-gil) and Myeongdong Station Store (134-1 Toegye-ro), both open until 10 pm. Drawers are bulky, so measure the space left in your suitcase first, and fill the drawers with clothes so no space is wasted. Mini tiered drawers are ₩2,000 (47K+ orders); the clear 3-drawer is ₩3,000 (7.4K) so you can see what's inside.
