I use it in different capacities all year long.
Anytime I see an area that needs motiviation, I use the treasure chest. And it works like a charm!
My most recent use for it, is the Secret Student. Sometimes, when we are walking in line I will announce that I am picking one, and only one, student who is the best student in line. It's that time of year when behavior starts to crumble. So it's necessary to pull out all the tricks, and this one is a keeper!