I just purchased one from Home Depot here in the states, that if you cool it down for about two hours before you load it, the temps will stay between 35-40 below actual outside temps, I went to Glacier national park the other day and it was only about 30 degrees, and ended up with some really ice cold beer..and it was real inexpensive, only $19.98 and will hold 9 cans of pop or other beverages as required, and if your not taking beverages, it holds a heck of alot of film as well, was able to get 60 rolls of 35 in it on our trip last week..
Dave