"Sis" asked what I had bought at Costco on Saturday, knowing full well that I'm a shopping addict. I did manage to contain my shopping urge (everything at Costco comes in a box that'd last me about 5 years.) I bought crackers, because you can't get crackers here without sugar in them. I can get boxes of saltines, but they are pretty expensive for plain old crackers, in Korean they're used as hors d'oeuvre crackers. (SPAM is treated as a luxury or gift item at certain times of the year, it's a different country.) I bought broccoli-cheddar soup mix, because canned soup here is fairly hard to find, most people make their own fresh Korean soup at home. I bought instant mashed potatoes because I like them when I want something quick and you can't get them anywhere else that I've seen. I bought a bath towel because you can't really find western-style towels (or bedding) outside of Costco and a couple of other places. I also bought a gigantic block of cheddar because it was only US$12 and I paid US$7 for a tiny piece in a Korean supermarket.
The oddest purchase to consider was a bulk-pack of mosquito coils, they were about US$5 for 90 of them in tins. I've been getting mosquitoes in my apartment since the beginning of March and it's not even really warm yet.
The best part of the trip was the train ride. The KTX high-speed train was quiet and spacious. A first-class seat for the one-hour trip was about US$30 for the round-trip ticket. As Tanya said, you make up for the few dollars difference in ticket price in free waffles (more like a waffle-cookie than a waffle) and complimentary bottled water. Oh and you get free sleeping masks.
(You should check the flickr pages to see what the sign at the top of the post reads, I'm sure it was a great deal but I wasn't in the mood for any.)