Store your most valuable notes in a LockNote. Hide your everyday notes in a safe place. Application and document in one: the mechanism to encrypt and decrypt a note is part of it. Secure, simple, independent. No installation required.
Locknote has a clean simple design. I would be very useful if not for a fatal bug where it occasionally fails to save changes. There is no error message or any other indication that it has failed. I have had it working perfectly for a long period of time and, for no reason, suddenly stops updating changes. If I use "save as" to create a new file, it will continue to work but will eventually fail again for no apparent reason.
Be careful - LockNote silently fails to save data. You can tell by watching the Modified timestamp ... when it fails it doesn't change. I lost critical banking login details. I am using KeePass now, which isn't great for handling text but at least it is reliable.