Okay, so taking into account everyone's suggestions, and attempting to come up with an appropriately difficult first day, you get... this.
Today, Team Expo needs to come up with
A) Gundam cosplay (as in a giant robot, not an emo pilot)
B) Crossplay of some sort
C) Open ended prompt: Tentacles. Don't ask, don't tell, but I want pictures of tentacles.
Team Expo: Well, there you go. That shouldn't be too hard for day one, should it?
Home Team: More ideas! Tomorrow morning I'll do this again, and post their findings.