What size cooler for regional work

40qt worked for me when I had a truck without a fridge. I just had it on the passenger seat and it was easy to tilt it a bit and drain the ice.

 

My experience with the Coleman products makes them NOT recommend. Koolatron is a better product for thermoelectric systems. They have both coolers and refrigerator products
More info here: Koolatron Branded Coolers. 12 volt Cool Boxes

 

I used a Koolatron 26 quart when I was out for a week at a time. Worked great for me - had a couple of those 40 qt. Colemans but they didnt last too long.

 

I use the Koolatron P-85 52-qt from Home Depot. Works great!!

 

The Coleman and many others are 12V coolers. You simply plug it in to a 12V outlet.

No ice to worry about so you have the entire capacity of the cooler for food, and no worries about draining it or getting food soaked in melted ice water.

The most common problem with coolers is the main fan. If that goes it doesn't cool.
And the most common problem with most brands of coolers is that they use a very specific fan. You have to replace it with their own fan because they are an odd size.

The Coleman, however, uses a common computer case fan. 92mm is the installed size, but a 80mm fan will do nearly as well and it is mounted to the heat sink fins. I have even used a 110mm CPU fan.
Most other brands need a specific fan that can only attach to pre-existing mount points.

I have tried a couple other brands, but the Coleman has always been the most reliable for me.

 

And that all depends on what you are intending to carry over those 5 days.
I can't fit 5 days worth of food in my big Coleman. But then, I would never try to keep fresh meat for that long in any case. I shop at Walmart at least every other day for fresh meat, fish and chicken. Veggies last longer, as do drinks.
But, 5 days worth in one shot? Never.