If you are planning to teach EFL (English as a Foreign Language) in Korea and thinking of what teaching material you shouldn’t bring activity books, handouts, songs, etc… it won’t be a good idea. You can try scanning the files onto a site that you could print when you need them. You can save a lot of space in your luggage. You can also buy the required books in Korea easily. Why carry a heavy load in your luggage when there are lots of English language teaching materials available in Korea. You could bring something which can be really helpful in ESL.
The best you can do is bring a laptop and some ink cartridges. Instead of bringing many books, a laptop would be much more portable. If you don’t have that option you can zip all your files and email them. You can upload all your successful lessons and activities onto a site like esnips.com; you can store and print them whenever needed.
If you are teaching in a private school then there are different books for different grades. These books are available at each school or they can also be ordered. Most of the school will buy all the textbooks you need.