I gave each team (4 people) a rubber band and four strings.
I told them they needed to use the materials to get the cups and move them to the table and build a tower! They could not touch the cups with their hands.
Most of the students figured out a strategy pretty quickly. The most popular method was to tie each string to the rubber band. Each person would pull on the string and make the rubber band wide open. Working together they would move one cup at a time.