For backing up settings, the easiest way is to add the files or directories you want backed up to /opt/.filetool.lst. Then with the control panel, use the backup/restore function and choose which device you want to store your backup on. Your case would probably be sda1 since it is a usb device. So enter sda1 when it asks for device. Then you can perform the backup. When rebooting, the backup should be found and automatically restored. You may have to use the "tinycore waitusb=5" boot code, but I rarely backup to usb so I am not sure if that boot code is necessary. The backup option is checked by default when shutting down or rebooting and that would result in a backup occuring each shutdown unless it is unchecked.
For storing extensions on that device, the easiest way would be to create a tce folder on the root of the drive directory (sudo mkdir /mnt/sda1/tce) and reboot. There are ways to do this without rebooting, but this is the simplest. After rebooting, when you use the appbrowser to fetch extensions they are automatically downloaded to the tce folder on that drive, and will be there next reboot. The "tinycore waitusb=5" boot code will probaby have to be used for the tce directory to be found.