For a USB drive, I would be more likely to use a bundle. Intended for offline distribution of a repository. Plus it is a single file, so you do not have to pay the transfer overhead of many small files.
You can repack your repo before you clone it onto the pendrive, and once it's there you can push and pull to it many times. Granted, pendrives are fast enough these days that copying an entire bundle every time is probably fine.
