My project has a number of test PCs which are 100% off-net. We use a USB drive to transfer files too and from these PCs. Some development happens during the tests on those PCs.
Readers who get here are probably also interested in using-git-on-usb-stick-for-travelling-code which has a great set of similarities. It probably won't work for my environment where there are two of use doing the sneakernet use/edit movements (i.e two separate USB drives), but it is a possibility.
It all depends on how much you trust the transfer drive, and if the tools can work when you haven't got it plugged in....