I got an Apricorn secure USB stick for storing passwords.
I woudl like to make sure that whatever file type I use on the stick will not create a temp file or so on the host. I am assuming Excel would be bad.
It is applications who create temporary files, not Windows.
And what's the connection between Passwords and Excel? Storing passwords in Excel means you need Excel to retrieve them. Plain text file with added personal encryption (like shifting letters, subtracting numbers etc) would be much better approach. Using USB key with built-in encryption would be the best (I don't know about your Apricorn).