The Big Swap: But what?

Zoe was walking down the hallway when she heard the announcement over the PA. She stopped, listened, frowned, and cursed. Then she started on her way, stopping as she passed Walter Smukmeyer. "Hey, you want to swap something?" She hadn't been able to think of anything else since the announcement. "Yes, but what?" Walter said, nervously. The feeling grew. The people in the school had an overpowering need to swap...which meant discussions like this were going on all over the school...and people weren't always making smart decisions. Finally, she blurted out...