First full backup on USB: Permission denied
You need to set ownership & permissions.
https://help.ubuntu.com/community/FilePermissions
If mounted at /media/stacyjane
sudo chmod -R a+rwX,o-w /media/stacyjane
sudo chown -R $USER:$USER /media/stacyjane
Note that the -R is recursion and everything is changed, do NOT run on any system partitions. All directories will be 775. All files will be 664 except those that were set as executable to begin with.
The -R parameter is recursive, so it will apply to all lower directories & files, but do not use on any system partition, just data.
see also
man chmod
man chown