The Core Principles of Economics - Learning about Opportunity Cost?

I use this lesson to introduce my students to one of the six core principles of economics - opportunity cost! Once students are settled in the classroom I have a question for the students to think about. Soon, after everyone had the chance to think about it, we began our discussion. Next, after quickly reviewing "scarcity," I ask volunteers to write their names on a piece of paper. I choose one of these names randomly. All students gather around as the chosen student receives two $1 bills. I announce that this money now belongs to the student. I don't want it back. It is theirs! Several choices are presented to the student and what comes next is one of our more memorable experiences in my economics classes. I am a 7th grade teacher, and I use this in my classroom but it can easily be used for grades 5-12, in my opinion. Enjoy!