What do you suppose those magical creatures are doing in lunch trucks at night?

I was getting my egg and cheese sandwich, and as I was walking away, I started wondering what happened in those locked up trucks at night. I wondered what kind of magical creature might make the truck it’s home, sleeping in hidey holes during the day, and then playing at night.

What kind of creature that is not an existing creature do you imagine? What does it look like? What does it do?