Building Challenges

Teaching a Spring Break camp next week (and working on the curriculum today .... shh! don't tell my boss!) and trying to figure out one more "Building Challenge" to add for the last day.

Here's what I have so far:

• Building towers & roller coasters to address the "How Big can you Build it?" question.
• Building airplanes & parachutes as introduction to the challenge of "Can you save our pilot, Egg-bert, from certain destruction (when I drop him off the top of the 12' ladder)?" More commonly called an "Egg Drop" challenge.
• Using the RAFT bin (named after Resource Area for Teachers but we always tell the kids it means 'Random Assortment of Fun Things' since it's just full of any reusable random materials I can get my hands on) to solve the challenge of "Can you move the ball from Point A to Point B without touching it?" Similar to this idea from PBS Design Squad, but with a PAJMZ-style twist, of course.
• Using the Crickets software for a "Build a Robot and Animate It" challenge

And here's where the problem starts. Camp is 5 full days (8 am - 2 pm). And I can make each of these challenges into at least a full day, but I need something for day 5.

One idea is doing a Solar Ovens challenge, and having them test their ovens with s'mores (and thermometers, of course). I'm a bit worried, because it's March and the weather can be temperamental. But if we do the challenge early enough in the week and can adjust the test time for whenever we get enough sun, it could be fine.

The second idea is having a "finish it up" day at the end of the week, where they can just work on making their designs better.

But I'm still trolling for a third idea. Any suggestions?