Be sure to sync the 8 GB iPod with iTunes. When you get the new one, connect it to that same computer, select "Restore from backup" and select the older one's backup.
Confirm that it contains everything you expect. Then, using the old iPod, go to Settings > Reset > Erase all content and settings. You or its new owner can then configure it as a new device.
I recommend that you sync it with iTunes on your computer. iCloud may be more convenient, but it could take a day or more to complete an initial backup or restore.
More importantly an iTunes backup is the only way to back up podcasts, audio books, music that did not originate from Apple, and photos or videos that are not in the iPod's Camera Roll.
Should I use iTunes or iCloud to back up my iOS device?
iCloud: Backup and restore overview
iOS: How to back up: