Each year I try to end on a good note with the teachers. They are such a huge part of making my program successful and many of them make sacrifices to their own time in order to reinforce my lesson topics beyond my brief sessions with students.
This year, I took my final lesson time to make a class gift for the teacher. The students used their thumbs and an ink pad to add colorful "leaves" to the tree I created ahead of time. The resulting artwork was attractive and many teachers got teary-eyed when I gave them their gift. This was an activity that was definitely worth the time and effort.
Here is the finished product. Full-disclosure, I got the idea from Pinterest (I'm actually incapable of coming up with good ideas on my own now that I have a Pinterest account!) You can find the original idea here.