.
If you get tired of adding 'persistence' at boot with your Debian.LiveUSB, you can tweak
the initial choice menu a little. Add a persistent mode stanza, to live.cfg,
and let this be the new default. You need to do this with another Linux, MOUNTING
the Debian.Live unit inertly as a bunch of files, rather than executing it as a live system.
Mine showed up at /media/sdc1/isolinux/live.cfg. YMMV.
Code:
label live-amd64-persistent
    menu label ^Live (amd64-persistent)
    menu default
    linux /live/vmlinuz
    initrd /live/initrd.img
    append noprompt cdrom-detect/try-usb=true boot=live config quiet splash persistence

label live-amd64
    menu label ^Live (amd64)
    linux /live/vmlinuz
    initrd /live/initrd.img
    append noprompt cdrom-detect/try-usb=true boot=live config quiet splash

label live-amd64-failsafe
    menu label ^Live (amd64 failsafe)
    linux /live/vmlinuz
    initrd /live/initrd.img
    append noprompt cdrom-detect/try-usb=true boot=live config memtest noapic noapm nodma nomce nolapic nomodeset nosmp nosplash vga=normal