Here's a trick for all you iOS 9.3 users. It's a way to password-protect items in the Notes app. It's a very useful feature, but the problem is that it's not clear how you go about the process. However, once you've seen how to do it, you'll be amazed how simple it is.
Here's what you do. Note that this process works on both the iPhone and iPad.
First, create a new note or open an existing note. Then, once you've done that, click on the Share icon at the top-right of the screen.
Note: You can still see the first line of password-protected notes (which is used as the title), so bear this in mind when using this to store data.
From the menu that pops up, click on Lock Note.
Now you get to enter the password -- don't forget it! -- and a hint. Also note that the default is to also allow the note to be unlocked using the Touch ID fingerprint reader. If you want added security, you can change this on a note-by-note basis.
When you're done, click Done. The first time you go through this process you'll be presented with the following warning.
Congratulations! You've successfully password-protected a note!
When you want to unlock the note, you get the option to use Touch ID or the password.
To password-protect subsequent notes all you have to do is to either enter the password or use Touch ID.
You can access Notes password settings from Settings > Notes > Password.