We recommend you only bring a light load of clothing and essentials with you to Korea (pack mostly relevant to the season you will be arriving in). You can pretty much find most things you will need within the country, though you might be limited to a narrower selection of those things. Remember, you will eventually be leaving Korea, and so will your stuff so the more you bring, the more you'll have to take with you or get rid of when you leave. And you'll likely want to shop in Korea.
Some BIG westerners may have difficulty finding sizes large enough for westerners when shopping for some items shoes and clothing, so bear this in mind when packing. Spray deodorants are notoriously difficult to find in South Korea, so perhaps it would be wise to stock up.
Here is list of items to pack for your quick reference.
Business casual clothes for work. refer to the article - Dress Code
Shoes for work
Hiking boots (can be used for winter boots, as well)
Copy of your teaching contract
International driver’s license (very easy to get)
Deodorant (Korean’s generally do not use western deodorant)
Women may be unable to get some of the same brands of feminine products, so you may want to bring a supply of these or any medication you are taking
Personal photos of your family, friends and pets
Prescription for your lenses (in case you need to replace them)
Books on Korean culture, Korean language, a Korean/English pocket dictionary, and a travel guide