Oh middle school - it's a mixed bag. The kids are so fickle, and the focus groups get so political.
You might want to try (depending on time of the year):
Mardi-Gras beads (with school colors)
Photography booth with a celebrity (solicit help from camera or AV Club)
(some of the larger party stores or Spencer Gifts have cardboard cut outs
of celebrities Elvis, Austin Powers, Shrek, or some pop star?).
Flavored popcorn (in case student council doesn't want to do popcorn - you can make it ahead of time and bag it up) cinnamon, apple, cherry - More recipes here from the Popcorn Board
Recipes with Popcorn
Air Brush or Henna Tatoos? - I recall a place where you could rent the equipment and tatoo stencils. Second thought - - Forget Henna - it's smelly and messy.
Wii booth - have a Wii demo booth. Bring the equipment along and an easy program (bowling) have the kids pay a couple bucks for "X" number of minutes to play.
Good luck - that's all I can think of without turning it into a shark frenzy - the hormones are running high and feelings get hurt quickly at the Middle school level. Simple is best.
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