Paper plates, Popsicle sticks, and a balloon are all you need to play Balloon Ping-Pong. (Not sure how sturdy the paper plates would be, but may be able to do something similar for a carnival/game night social event theme.
Rainbow Bubble Snakes - Need: Half a waterbottle, rubberband, bubbles (dishsoap/water), food coloring, sock. Steps: Dip sock held by a rubber band on the water bottle in food coloring in dish soap and food coloring and blow. Have fun!
33 Activities Under $10 That Will Keep Your Kids Busy All Summer