five day huh, well just came from Costco and they had a six day. First Liar doesn't stand a chance.
We save all plastic pop bottles, wash them, refill with water and freeze them. Ice won't last as long as with the gallon milk jugs but we can stagger them around to spread the cold better and fit nooks and crannies better.
Since I also use bottles instead of a bladder when hiking or hunting, I fill my bottles 1/2 full and freeze, then top it off the morning I leave so I have good cold water most of the day.