A repository does not always have all annexed file contents available.
When you need the content of a file, you can use "git annex get" to
make it available.

We can use this to copy everything in the laptop's annex to the
USB drive.

	# cd /media/usb/annex
	# git pull laptop master
	# git annex get .
	get my_cool_big_file (copying from laptop...) ok
	get iso/debian.iso (copying from laptop...) ok

Notice that you had to git pull from laptop first, this lets git-annex know
what has changed in laptop, and so it knows about the files present there and
can get them.