My friend, Ellen and I brainstormed this one at coffee the other day, as an opening day activity.

Hand each member of the group an envelope with 3 to 4 post its, each with a different number on them.  Have the group combine their post its, and place them on a generic number line (not labeled) posted on the wall in the classroom.  Once all groups are finished have them check the work of another group (each group will have their own set of numbers), or do a gallery walk, looking at all the number lines in the class. 

The numbers should include decimals, fractions, integers, square roots, pi,simple cube roots, etc.  NO CALCULATORS allowed.