Apple - Export Keychain Items is not enabled from File menu of Keychain Access

You can only export one key at a time, or one key and a matching certificate. It will be encrypted upon export and can only contain one key.

If you need to move an entire keychain to a different computer, look at ~/Library/Keychains - example login.keychain (in finder, cmd + shift + g, paste path, go)

It can be added to another machine and you can change the password of the keychain.

It seems that only certificates can be ex-/imported, but not passwords.

You could copy and rename your keychain though, as described in apple support document. Then open "Keychain Access" and you will see your renamed keychain in there. Now you can copy/paste whatever item you want from one keychain to another (e.g. to your login keychain). Once you