An idea that falls into the "why didn't we think of that" category: picnic baskets lined with insulating Styrofoam and rattan baskets with galvanized liners to keep food and drinks cold all afternoon:
Above: The Rattan Party Bucket with galvanized lining; prices start at $40 for the small at C.S. Post & Co.
Above: The Peterboro Tailgating Cooler Basket is $54.
Above: The Peterboro Ice Master has a removable Styrofoam insert to keep food cool; it's $55.
N.B.: This is an update of a post originally published July 26, 2012.
For even more options, see 5 Favorites: Portable Coolers.