I've found that predicting how many/which people will show up to various events and how late people are going to be to meetings are both good prediction formats. They're easy to formulate, and for most people they will come up frequently in day to day life. Also, somewhat similar to ChristianKl's suggestion I've found "I will get at least a [letter grade] on [assignment]." to be both easy to generate and at least semi-relvant to the average student.