Files are often very difficult for beginners to visualise. I use a roll of exposed film to denote a sequential file. This has lots of little compartments the same size one right after each other, and they are even numbered. In order to demonstrate the difference between the name of a file and its handle in the program, I put a piece of paper at the top with two names on it, one that the program sees and one for the file itself.
2016: They have no idea what that roll of exposed film is supposed to be....
