I have an Igloo 150 Qt ice chest that I fill with blocks of ice. We use it during August antelope and archery deer hunts when the temperature is in the 90's during the day. We make sure we keep it in the shade and don't open it until we need to ice down an animal. We have kept ice blocks in it for over a week and still had ice even after cooling a deer or antelope when the initial cool down melts the blocks down quite a bit. We just make sure there is always a layer of blocks in the plastic bags under the meat to keep it out of any water, keep the drainplug open.
One of the drawbacks is of course it is very heavy.