Buckle up - Seatbelt Keyholder --- what a great idea for someone who's constantly misplacing their keys. Mount the buckle to the wall by the door and they'll never misplace their keys again! Visit a salvage yard and grab enough for the whole family.
Make a backyard bowling alley. Add food coloring to clear plastic bottles of water. Use party streamers as lane margins. Add glow sticks for night bowling. (These would make great outdoor table nightlights also with the glowsticks, gonna try it!