I had a brainstorm a couple of years ago about the problem of keeping fresh eggs and frozen broilers cool at the farmers’ market: salt-water ice. A saturated solution of salt water freezes (or melts) at zero degrees Fahrenheit. Not only is this cold enough to keep frozen broilers frozen, but it’s cold enough that water condenses as frost, not water, on the sides of salt-water ice containers, and frost doesn’t drip onto the egg cartons.
(One the ice inside the container melts, the ice on the outside will melt, too, but it works like a charm until then.)
This works so well that I’m surprised everyone hasn’t always used it. Blue Ice, for example, claims to be “colder than ice,” but it doesn’t seem to be. (Condensation drips off Blue Ice, rather than forming a layer of frost or ice.)
Used plastic soda bottles make good salt-water ice containers. To make a saturate salt solution, add one four-pound box of pickling salt to 1.5 gallons of hot water and stir until as much of it has dissolved as is going to. Pour into used plastic soda bottles and freeze in a freezer that’s below zero F. When you need to keep something cool, toss these bottles into the cooler, then back into the freezer when you get home. Simple.