I carry game and fish on ice for days in large coolers on my boat. A couple of tricks:
If you line the bottom of the cooler with a fitted piece of ensolite and then put another piece over the contents , just under the lid, it really helps. Ensolite is the closed cell foam used for sleeping pads when backpacking, about 1/2 inch thick.You can cut it out to fit against the sides of the cooler tightly, and cut a notch in the bottom piece by the drain, takes just a couple of minutes with a pocket knife. They wash up good for reuse.
Another thing is to cover the closed cooler with.a space blanket, silver side out, and secure with a bungee cord. It helps keep the sun off it and adds a trapped space of air around the outside. It is easy to take off to check/add ice.
Both of these make the ice last a lot longer, and keep the temp more consistently cold throughout the inside of the cooler.