Question: In Western Europe, we currently have a long spell of warm and dry weather. The perfect moment to combine sunbathing with working from home. However, outside in the sun, the legibility of my laptop screen is greatly reduced when compared to inside the house/office, even when I maximize the display's brightness. Are there any tricks I can use to increase the legibility (and ultimately my productivity)?  

I'll share one trick I often use, but I'm definitely interested in more suggestions.

Answer: 
The cardboard box suggested by Glorfindel, and improved upon by Stan's comment, is fantastic. I have another suggestion that can be used with the box or by itself.

Wear a dark shirt, and make sure whatever is behind you is dark. (A wall, a shaded forest, etc.) Much of the reason you can't see the screen is because of reflected light. Therefore, if the screen is facing something dark, there will be less light for it to reflect, and you will be able to see the screen's display better.
To increase the legibility of a computer screen, arrangement should be made to control the fall of run rays directly on the computer screen. This can be done by covering the top of the computer by some wooden surface or cloth , in such a way that the area of the wooden surface or the cloth is more than the area of the top surface of the computer.