After the train crash, the teen characters discover cube-like items. One of them states it looks like a Rubik's Cube. The movie itself takes place in 1979, but the Rubik's Cube, although invented in 1974, was not licensed to sell in the USA until 1980. It was not even called a "Rubik's cube" until 1980 (prior to this, it was known as a "Magic Cube").
Wait for about 2 minutes when the credits roll and you'll see the kids' completed zombie movie - it's about 5 minutes long and fun to watch.