JK’s posts a reminder you can use Windows Briefcase to keep files/folder copies on your USB Drive in sync with their source files on your machine. I use Briefcase for this all the time as, although basic, it allows you to sync selected folders or individual files and will work on Windows machines with no software install.
You can also have separate briefcases sync'ing to different machines/locations on one drive. I have a USB with crucial home and work files sync’ed so I can access/edit those files while away from either location. Then it’s 1 click sync to update the source files.