DIY: Bubble recipe and refill station. Love the idea of reusing plastic cups from restaurants as the containers. Keep the bubble solution confined to one big refill container, and no worries about leaky, yucky containers hiding all over the house!
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!