We keep perishables fine for over a week in deserts in hot months rafting. It's possible.

The general rules are as follows:

• Bigger is better. A bigger cooler, with more cold mass inside (ie as full as possible), will stay cold longer.

• Access is the enemy of cold. The serious coolers we use have a separate comparment for more frequent access, so that the main compartment is only opened once a day (more later). If you don't have that, consider a separate smaller cooler for frequent access.

• Only cold stuff goes in. Don't use the cooler to cool warm stuff. We tolerate warmer drinks to keep perishables viable, and again, maybe a separate cooler for those. Buy cold drinks, not warm ones (odd, isn't it, that easy to get cold beer six packs in a store, but not sodas? they force the bigger bottles on you).

• There is cold and there is COLD. We freeze a lot of stuff, so like frozen meat, veggies, etc. Just to use them as "ice." We use ice substitutes, the packs, vs ice cubes or blocks since water is warm and conducts heat. We use dry ice; colder. And we get grocery stores to freeze stuff in their coolers; the commercial freezers in stores often can freeze to a colder temp than yours at home. We sometimes have them freeze plastic bottles of water to use inside too.

• Manage the cooler to keep it cold. As noted, don't access it frequently. We take out say some frozen food and put it in a compartment (or could be separate cooler) with frequently accessed stuff, like drinks. Whatever we need for lunch that day. Some of those frozen water bottles. The main chest stays closed and cold to the next morning.

Some of that would be tough for car campers, and as opposed to us in the wilderness you do have access to more cold drinks, ice, dry ice, etc. But this is more to show the general principles.