Korea is a fast-changing country. There’s a possibility that the store that existed a year ago suddenly disappeared or changed open hours. You can check the hours on Naver Map or Kakao Map, or call to see if it’s open. (Google Map doesn’t really work in Korea due to national security issues.) It’s better to make sure the store is in business before you leave than to go in person and find out it’s closed.
Sadly, Korea is facing microdust issues. Some days the sky will be clear but some other days will be covered with dust. Make sure to check the air quality through apps like IQAir and Misemise. If the air quality is bad, buy a mask in one of the convenience stores. Masks with a KF94 sign are better with microdust.
Korea is a highly populated country, especially in big cities. One of the privileges that tourists have is that they don’t have to go to work or school. In other words, you can visit places when there are fewer people: weekdays, opening hours, and in the middle of the day (at around 2~5pm). It might be better to avoid weekends, lunch or dinner times, or you might end up being stuck in the crowd or waiting in lines.
In summer, indoors can be freezing due to the air conditioner. The room temperature has risen a little these days to save energy, but it can still be cold in some places. In particular, it’s so hot outside that you could catch a cold due to the temperature difference. It’s the same in spring and autumn. There’s a big temperature difference between day and night. To sum up, it’s better to carry a jacket regardless of the season.
Finding a trash can in Korea can be harder than you think. There are trash cans, but you won’t see them often. It might be easier to just carry a plastic bag and put trash in it. When the weather is nice in Korea, it’s really nice to walk around while eating and drinking something. But then, you might not find a trash can and end up holding the trash all the way to your place.