I heard there are squrish flash drives that can save your entire desktop from some teachers and librarians at school. Is this true?

I would not have a clue about that but if you're looking to hide stuff from people at school Alt Desktop is a good program (I don't know where to download it sadly). However I have seen it in use and basically it works by just pressing a some kind of hotkey (or button attached to the program) allowing you to change to a clean desktop showing none of your games in the start bar, you could also open up a word document or something in this desktop to make it look as if you're actually doing work. You then just press the key again to switch back.

External hard drives are kind of like that. But they are also expensive like 80 -120 dollars depending on size.