Balloon Wall as a photo backdrop. Tape the strings at various heights to create a wall of balloons. Instant backdrop in any color. Guests could have their picture taken in front of the balloon wall by Mary maybe, sort of like a photo booth.
Mason Jar Drinks - for mixed drinks, lemonade or whatever. Just divide your drink into mason jars, put the jars in a large tub and cover with ice for easy self serve drinks. I bane a bunch of jars with the lids and all.
Light Up the Dark ~ Fun party idea. Cut open a glowstick and shake it into an empty bottle. Whirl and swirl it around for fun glow in the dark colors. You can also add some water or oil to the jar to give it bigger and a more even color.
If I had a pool I would totally try this out. Put a glow stick in a balloon for pool lanterns. Pool party on a Summer night! I think this could work pinned up on the fence of a backyard without a pool, too, so really great idea for any outdoor BBQ/party!