I learned this lovely tip from Martha Stewart:
#5 Here is a quick way to chill your drinks before an unplanned party or when on a camping trip. Place your bottles/cans in a bucket or container and add a layer of ice followed by a layer of salt; repeat the ice/salt layering until you almost reach the top. Fill the bucket with cold water to just below the ice line. Thanks to the salt the water in the bucket will be colder than normal, chilling you drinks in less than 10 minutes!