Generally, you can find anything in Korea but if there are specific brands you like to use, you may want to bring them. Also, if you are placed outside of the city, specific items may be harder to find. The following is a general list of things you may want to bring to Korea:
Money, Clothes that are suitable for all four seasons, Shoes that are suitable for all four seasons, Electronics, Chargers and Adapter (for 220V), Underwear, Toiletries, Cosmetics, Razor, Medicine, Watch, Umbrella, Books, Birth Control, Feminine Products, Deodorant, Dictionary, and/or Hair products.