As soon as I decide when and where I'm going, I check to see what's required for travel to that country. At this posting, I needed vaccination information and a current K-ETA (Korea Electronic Travel Authorization) to enter South Korea, in addition to my passport. I checked my expiration dates for all these items and my global entry pass. I'm good to go! As a backup, I have printed and digital copies.
To make life easier, I also studied and downloaded a guidebook full of great ideas, and added tourism, communication, and navigation apps useful in South Korea to my iPhone. All these items (sans iPhone) are stored in a safe place until time to travel!
One more important thing to check is medications. I don't want to run out of allergy meds while on the road!
