I recently had an outdoor party for my child and her friends. I used a muffin/ cupcake tin to put all the cups of water in, so that they wouldn't spill when I carried them outside. It was nice because everyone got their water at once, rather than me bringing outside only what my hands could carry.
Or having to deal with a pitcher and piles of cups! Very civilized! Great birthday party spill-saver.
More: Hacks for birthday parties