Popcorn box
There are plenty of recipes for popcorn boxes online, but I created ny oen in the end. The best part is you don't need to trim down your A4 card stock, you just start scoring.
Score along the long edge at 7cm, 14cm, 21cm and 28cm. This will leave a little flap at the end that you will later use to glue your box together.
Then score along the short edge at 5cm and 15cm.
Now score a flap, this would be at about 20cm, but I just used the measurements on the other side of my trimmer and scored in 1cm.
Now trim your box, it is hard to describe I will just show you with photos.