It's my son's birthday party tomorrow and we were going to have it in the park. However, we wanted to have ice cream with the cake. So, I thought about picking up some dry ice and putting a chunk in the cooler with the ice cream to keep it frozen. However, the dry-ice guy tells me that it'll probably make the ice cream rock hard. So, I wonder.. could I get away with just ice in the cooler? Would the ice cream stay hard enough do you think?