 Potato salad is also on sale this summer, with potato prices down more than 4% since the last Fourth of July. Potato chips and salsa have gotten more expensive during that time, but guacamole prices have come down. If you're buying soda pop for the cookout, two-liter bottles have gotten cheaper. Drinks sold in aluminum cans, however, are more expensive, thanks to the rising cost of packaging. Scott Horsley, NPR News, Washington.