Use MadLibs to create a spell.
prepared paper sheets to fill in the MadLib blanks
pens/pencils
This is a neat Madlib that goes along perfectly with a potions class that can be found at the harrypotterfans website.
Because it's an online project, you can retype it in a text file to make it easy to use on paper.
Make sure you know how to explain all the different types of words!