I race with one of these. http://www.icevest.com/

Built by a racer for racers. Three packs, one on my back and two on my chest just before you get in the car will last almost 35 minutes in 90 plus weather. If you wet a t-shirt down under the ice-vest you will almost freeze your ass off on the warm up lap, then I don't know it is there until after the race. The packs will recharge (refreze) in a cooler with ice and water in it in about 20-30 minutes or in the motorhome frezer in about 15-20 minutes.

I highly recomend this vest.

Jon