Do yourself a favor and go to the local thrift shop, and find a older Igloo playmate cooler.(circa 89-92)
Then combined with 32oz frozen Gatorade bottles(I used to use 3) or ice paks they stay colder much longer than the new ones
I bought a new one once, fell off the shelf and broke, the old ones just keep going and going.
try and put the ice above the food when possible, it'll keep it cooler.
as a side note I would use my 32oz gatorades as my water for the day as well, and generally when on the dash,
or my massive cup holder, it would be completely melted by 10:45.(with an start on road time of 10)