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!
Decorated easter eggs - I think you need a hollowed egg for this. Write a message on your egg in clear wax, then add a little white vinegar and a little food colouring to a glass of warm water, and dip your egg into the solution.