Provide each group of students with two jars - one filled with tiny pasta and a second that's empty, as well as a variety of measuring tools: balances, rulers, graduated cylinders, etc. The group is to use the allotted time to determine the number of pieces of pasta in the jar.
I have used this at the beginning of the year and when forming new lab groups - a chance for the team to work together to find a solution. A good opportunity to observe students and their ways of thinking.