plain text files and your favorite editor, whatever that is.
things that should be encrypted are either gpg encrytped or put in my password manager.
Bonus if you format your plain text with markdown or asciidoc or whatever your fav. plain text markup language is.
Don't make it more complicated than it needs to be.
Put it in a VCS for super double bonus points :)
me personally: Vim, asciidoc and in a fossil repo.