There is a really good showdown of high end coolers on YouTube, I'll see if I can find the link.
We have one of the old Coleman X-Treme cooler which has walls about 2" thick. (Got it a garage/tag sale for $20) Using ice blocks, it will last about 4-5 days in summer heat. We tended to use this cooler for meat though, and only opened it once a day. New TT has a much larger fridge, so we don't use coolers much at all anymore. Maybe one for beer and pop if we have a lot of people on the site.
ETA: Here is the link to the one I watched.
While looking this up I came across several others that do the same thing.