[cMags]

I would use a bubble mailer - they come in pretty small sizes - it should protect the drive and keep it from getting tossed into the automatic letter sorters that could crush the contents in a normal envelope. It may cost a few coins more than a standard letter, but worth it to make sure it gets there in once piece.

Edit: also, FYI, I moved this thread to the Lounge, as it doesn't pertain to tips or tricks for building models.