Go to wallmart. Get a styrofoam cooler. Get 2 x 5 lb bags of ice and some newspaper. Stick the ice below and above and wrap the rodents like crazy in newspaper put it between ice and stick it in your trunk. You will be surprised how cold that keeps it. Should be less than $15 for the whole thing and easier than trying to find dry ice. This is of course if you can't find dry ice. If you do have dry ice then get that and wrap it in tons of newspaper and stick that in a cooler in your trunk.