There are a lot of statistics about the fact that taking breaks actually increases your overall productivity. So breaks are supposed to be restorative.
And the "Learning How to Learn" course material emphasizes the importance of switching between focused mode and diffuse mode. (with "diffuse mode" representing breaks)
But what exactly should you be spending your time on during a break, in order to maximize productivity? (though exclusively focusing on productivity isn't so good; hopefully we can improve overall well-being too)
ABSOLUTELY AVOID SCREENS. Shut the laptop and stay off the phone.
You can Google a few things: