At this booth, put on by Operation Smart of girls inc., people were challenged to see how tall of a tower they could construct with marshmallows and toothpicks. They hoped people would start experimenting with different designs and see which were stronger.
For anyone who wants to try this with their kids, here's an online lesson plan from www.sciencedays.org that gives a little more information.
Here's the beginning of a tower:
Here's a finished tower.