Just ended my South Korea trip. It was a nice trip where I visited Jeju Island and Seoul.
The culture at Jeju-do island was rich and there were lots of stories behind many of the things that goes on there. Like the stone culture there, the beautiful nature. Although Jeju is a small island, the bus service is quite an hassle as they are mainly in korean, less the Airport Limo Service. Taking a taxi around the island would be the ideal choice as it would allow you to cover many of the attractions in a short period of time. I hired an taxi guide for the whole day at 150,000 won.
The seafood is fresh there and very nice. Attractions mainly require a nominal fee for entrance fee. Convenience shops are dominated by GS25 and CVS 4 you.
As for Seoul city, shopping was good as it was the Korea summer sales. I brought a shirt for 5,000 won (Actual Retail price: 35,000 won) Food wasn't cheap as it goes around for 12,000 won for a normal set lunch. The interesting thing about shopping in a departmental store in Korea is that Plastic bags are not given. Hence we have to wrap our purchases using discarded cardboard boxes that were provided.