RobertSmalls -
Here's a less efficient way :
1 - Get a fishing jacket.
2 - Get a bunch of $1 mini ice-pack thingies that look similar to this :
3 - Fill every pocket with them.
4 - They only last maybe 2 hours. So, for the long 8 hour trips, keep a bunch in a cooler.
I get the rigid ones in hard plastic because I am afraid of leaks (but the hard plastic ones can also leak at their cap). The problem with that is that I can't have them between my back and the seat, otherwise I could risk serious injury in an accident.
CarloSW2