Challenge your members to make a square from 2 paper circles
http://www.whatdowedoallday.com/2015/06/geometry-magic.html - video link showing how it's done
2 paper chain links per person
Form one strip into a circle. Tape.
Loop the second strip through the circle in the manner of a paper chain. Tape.
Securely tape the two circles together. Important: tape loops together on both sides.
Carefully cut one circle in half lengthwise. Now you have two loops connected by one long strip
Cut the remaining strip down the middle
Watch the magic and be impressed again and again: