The best option is going to be a USB drive that has an external key entry feature. Kingston IronKey has these and its as simple as enter a key and plug in. I use them at work and it works on all the major OSes. They’re not cheap though so if you want or are looking for a free solution then something like VeraCrypt portable and an encrypted container will be your next best option.
How about you tell me why instead of just saying “TeRribLe AdViSe.”