Cookie Sheets as "Busy Trays"

I recently discovered that cookie sheets aren't just for baking cookies. Because they have a hard, magnetic surface, a lip so that things don't fall out, and are lightweight they have become my girls' "busy trays" for activities we do at home and on the go. A few of my favorite ways to use them are listed below.
Craft station for easy cleanup. 
Magnetic Board to practice forming words.
Great place to do puzzles on the go.
Perfect surface for writing letters in shaving cream.
Great for writing letters in sand or sugar.
Perfect surface for Wikki Stix.
Rainbow sensory tray to be used with sand or shaving cream.
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