I have students try and find how many ml are required for a soda to stand on its side. It's one of the many ways I teach about center of mass. I do let the students drink the content which they enjoy. That, and soda isn't allowed in the classroom except on this day.
Graphing Trigonometric Functions. Text books make graphing trig functions so complicated. I have simplified the process so that even below average students can follow the process easily and graph trig functions without frustration. I have passed these trig notes out to absent students and NO explanation was necessary! Trig graph paper also is included.