Use a bag of cheap ice to pre-cool your cooler.

Yes, do it. An hour before you pack, toss a bag of ice (or a couple of frozen water bottles) into the empty cooler, close the lid, and walk away. The ice doesn’t need to melt — it just needs to chill the walls and insulation so your real ice doesn’t have to do that work later.

Don’t use your good ice for this. Get the cheapest bag you can find, or freeze tap water in old jugs. After 30–60 minutes, dump the pre-cool ice (or save it for drinks if it’s still solid) and load in your food and fresh ice. Your cooler will stay cold noticeably longer.

If you’re really in a hurry, you can skip this step and just add extra ice. But for a long trip or hot weather, it’s worth the minimal effort.