Pack the potato salad into a cup.
Chop the broccoli into small pieces.
Stick the broccoli into the potato salad around the edges to make a wreath.
Place the wreath into the bento box and decorate with picks, crab stick tinsel etc. to finish.
This is how it looks inside the bento box. You can find out how to make Santa and the reindeer at: https://cookpad.com/en/recipes/150392-christmas-character-bento-with-santa-claus-and-a-reindeer
Here I tried putting some frozen gratin in the center of the wreath.