Thats a good start for a backup script. Iceweasels bookmarks etc are in /root/.mozilla so backing up /root already takes care of that.

Now here are a few suggestions, though it might be a lot of work making a script with these functions added.
Backing up directly to USB/SD is
not really a good idea unless the USB/SD card is formatted ext2/ext3. The reason being is that fat/fat32/ntfs file systems cant handle 'long file names' so it'll rename or shorten filenames. That could potentially create lots of problems. Secondly fat/fat32/ntfs file systems automatically change every file's attributes and marks
every file as an executable.
Now there is an easy way around that however. Just have the script backup everything you want backed up, but have it copy them to say /tmp, then have it tar or zip them into a backup archive, then have it move the backup to a USB stick or SD card. Once the files are safely tarred or zipped the contents are safe from the issues i mentioned above.
You could easily make an .xap or .3mx package also. Using MC make a directory in /tmp called backup. Now copy /root to /tmp/backup. That leaves you with /tmp/backup/root. Now mkdir /tmp/backup/etc/jwm , then using mc copy /etc/jwm/jwmrc to /tmp/backup/etc/jwm. That leaves you with /tmp/backup/etc/jwm/jwmrc. Now copy the mkxap or mk3mx script into /tmp/backup. Then cd /tmp/backup and run ./mk3mx my-settings-bkup root etc ...you now have created an .xap or .3mx installable backup file.

You can then safely delete the backup folder in /tmp
after you move the .xap or .3mx backup package to your usb/sd card.
Cheers.