Tell me one thing to do over the winter vacation

I’d say start compiling a list of people you want to network with in an excel file. Take time to find them and their emails, then make drafts is a good start imo. I’d also start reading new articles daily and maybe freshen up your resume.

Good time to study technicals if you haven't yet!

Studying finance, following the news, reading books.... they can all be done after you go back to the US, too. During your vacation, which is already too short to do anything really big, just do something that you can only do in your home country. Check out parts of Seoul you haven't been to, visit regional cities in the South like Busan Daegu or Jeonju, and at the best of your ability network with professionals in Korea and hear from them their experience and advice.

Also, one thing I recommend is taking the driver's license test. 3 weeks is enough to go to local academies that help you prepare for passing all three tests (written test, functional test, and actual road test). Better knock out the mandatory to-dos at your early years when you have enough free time.

Go to pc bang

If you think winter break is a “waste of time”, you clearly aren’t living life properly