This may be common sense to some people but for those of you that have never done this you can pack a food cooler for about week. We used to go on a 8 day canoeing trip and the cooler would last the whole 8 days. Usually by mid-afternoon on the eight day the final piece of ise would be about the size of baseball or the water would still be cold enough for the day. Of course the first thing you need is good cooler.
You first need to freeze all your food, anything that goes in there should be frozen. When you're freezing it try and freeze it so you can pack stuff in there as tightly as possible. If you have steak, hamburger, chicken or whatever take them out of the packaging and put them in zip lock bags, Get all the air out and and try to mush the separate bags together to form a block with them. The hamburger for example works well to form around odd shaped chicken.
For ice you'll want to freeze one gallon plastic gallon jug (2 if you have big enough cooler) and a few quarts. How manny quarts depends on how much space you have but you will want a few of them. No cubed or loose ice to create water, it has to be in containers. Pack everything in as tightly as you can in the bottom of the cooler keeping the very top as level as possible. One of the keys here is trying to avoid air pockets below the top of the food .
Always keep the cooler covered with a blanket and and in the shade if possible at all times preferably one that is white except of course when you open the lid. When do you open lid do it quick and be sure you know exactly what you're going in there for. You want to make sure you keep the top even and everything as tightly packed in there as possible so you may want to occasionally repack it real quick. If you have old wool blanket cut a piece out that you can use to put over the top of everything inside the cooler. I never used cotton or other material and I don't think that will work well unless you keep it real dry. Take out the quarts if they have completely melted.
That lasted me and another guy with a regular sized cooler, one gallon jug for 8 days in 85 degree weather in the beating sun most of the day. Now the cooler itself was always tightly packed on both sides so during the day the only thing that was really exposed was the top. None the less 8 days is pretty long in those conditions.
One thing to note is this doesn't keep things super cold once once it thaws. Be sure if you have chicken or anything else that goes bad quick to eat that first and such items should be as close to the block as possible.