can you take a cooler with you?
you could pre-make the soup and put it in ball glass jars to take with you.
and then you can just get more ice from a convience store when your ice melts.
my mom had this thing that you plugged into the wall and then you clipped the other end onto a side of a cup. there was a metal part that heated up and would heat whatever was in the mug. look for that at a radio shack or some place like that.
that way you could heat up your soup. or fill the sink with really hot water and submerge the jar in the hot water to heat it up.
you could get one of those cheap stryro-foam coolers if you dont have a real one.
buy bags of fruits like apples and oranges. buys some nuts to take with you.