Wow! What a great idea, and all it takes is the addition of a rain gutter. This makes the perfect trough for ice and beverages, right where you need them. I like how in the first picture, it appears they attached the rain gutter from the inside, versus the second picture using brackets. This gets me thinking of all kinds of different uses for this idea, herbs.. lettuce... or full of water and floating candles. I think it would also be nice to set the gutter a bit lower, so you could have a loose board to act as a cover when you don't need the trough. I know what's going on my next picnic table! You could definitely get this done in an afternoon, better yet - before this weekend! Good luck, let the rest of us know if you tackle this & how it went.
Special thanks to LifeHacker and PicnicTablesOfHouston for the idea & pictures.