macOS (10.9 Mavericks) created a new keychain "Local Items" for me that can't be deleted. What's the idea here and why is there a second keychain in addition to my login keychain?
If you mean the keychain that is called Local Items in the U.S. English locale, I think it is used for keychain items that are eligible to be synced with iCloud Keychain.
If the iCloud Keychain is subsequently disabled, the iCloud keychain highlighted in the screenshot above is replaced with a "Local Items" keychain that has the same contents as the iCloud keychain. Any items added to the Local Items keychain will be pushed out to other devices when iCloud Keychain is re-enabled.
I have never enabled iCloud Keychain, but I also have a Local Items keychain. It contains about half of the keychain items from my login keychain, or mostly web form passwords. The Local Items keychain does not seem to correspond to any file and it cannot be deleted.
There is a difference between the local items keychain and login keychain. Make sure to pay attention to this fine detail when an error message pops up.
If you have a local item keychain issue, here is what I did to resolve my issue that nothing else would fix.
The name of the folder it gives is not the name that will be in there, mine only had one folder. I had then move it to the desktop and restart after that another one replaced it. Then I had them delete the folder that I moved, restarted again and everything was fixed and no longer a million boxes popped up, asking for a local item keychain...
Although the "Local Items" keychain cannot deleted, you can delete individual items stored in it.