Every poster must get out of the box, and they must use whatever they have to escape the Box.
They get to leave
Also, you have the option of simply dying in the Box, but you have to use the items you are given to do so.
In addition, the rule of cool can override other rules.
Example:
Poster A wrote:I am given a chainsaw.
I cut the box open with my chainsaw.
I leave a pen.
Poster B wrote:I am given a pen and a piece of paper.
I write a letter to the military to free me from the Box.
I leave Ciary.
Poster C wrote:I am given Ciary.
I hug Ciary to gain unlimited power, and thus I blow a hole through the Box.
I leave a painting.
I am given a painting.
It is a painting of Cronus eating his children, so I bring him to life with my magical powers and Cronus takes me out of the Box.
I leave a Troll.