In the esky, icebox or fridge, whatever your coldest is. You might have to fight for the beer space though. We breakfast on melons and strawberries wizzed up in a blender, so I make two litres of this fresh before heading out and store it in my coldest box. The second coldest one usually holds the fresh salads and other fruits. Or I might put some grapes in the coldest one to eat first nice and cold. Keep the fruit and veg in the fridge overnight before you leave and then make sure you keep the cold boxes as cold as you can as long as you can on the trip and they should last nearly as long as they would in the fridge at home. If it's really hot out though you'll need a good reliable fridge and plenty of power for it. I've never had a fridge but have had good results keeping esky's cold in moderate weather, keeping the esky out of the sun in the coolest part of the car or the campsite as possible, covering it with towels etc if necessary. If you want to beat the elements though you need to go for more technology, as a rule.
You could also go for the less perishable stuff, whole pumpkins, potatoes, carrots with their tops on, green bananas that will ripen on the trip, greenish tomatoes will do the same, and even hard avocadoes (usually) ripen in a few days, especially if you keep them with the bananas. Whole watermelons and canteloupes still need to be kept cool but will also keep longer of course than those already cut.
A few ideas, hope they help.
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