Constitution Day is October 17. All classrooms (really not including you, necessarily, but it couldn't hurt) are required to conduct a lesson on the U.S. Constitution on that day. I really like working on concepts around government with students- it's a topic that is way abstract for them, but so functional and important to learn. Try starting with this classic available on YouTube- Three Ring Government:
Kids love Schoolhouse Rock videos- they are catchy and get stuck in their head, thereby utilizing some brain-based learning techniques. Kids think they are quaint but I totally remember watching them with my Saturday morning cereal.
A good follow-up to this activity would be a sorting or graphic-organizer-based lesson, or a wordsplash with some of the vocabulary and concepts in the clip. Here, also, is a good online sorting activity.