To control when the save is updated or not updated.
Puppy needs to be running in pupmode 13.
To make it do that there needs to be a specific command in the boot loader menu config file entry.
Do not know what boot loader you are using to boot the Puppy install.
But it is probably using one of these boot menu config files.
grub.cfg
menu.lst
Find the file on the drive.
open it in a text editor.
Look in the entries for a pmedia= command.
change this to pmedia=usbflash.
Save change.
REBOOT.
Now it should be running in pupmode 13.
Should be a save icon on the desktop.
The save will update when you click on this save icon.
Other controls can be set by using the Puppy Event Manager -> Save Session
Set save interval to 0 minutes, so it never auto saves at a set time.
Set to ask at shutdown to save or not save.
Then it will only update the save, when you click on the desktop save icon.
At shutdown, when asked, you select save.