They might not be available in your area, but here in the west, especially in the northern Rockies, there are lots of bear resistant panniers made for horse packing. These are boxes that are hung from the packsaddle, one on each side of the horse. Check the Interagency Grizzly Bear Committee list of certified bear-resistant products. Go down past the backpacking containers to "Panniers and Boxes" and "Coolers and Dry Boxes."

I suspect you really don't need to keep all the food at the campsite when the car is away, just enough for the day's lunch. In fact, I'd think a Bear Vault (relatively inexpensive) would be more than sufficient for this purpose. Just make the day's lunch at breakfast time, stick it in the Bear Vault and keep it in the shade. If you really need to keep the lunch cool, put a wet towel over the Bear Vault for evaporative cooling. You may have to re-wet the towel mid-morning.

I've had a block of ice in a cheap cooler in a closed car parked in the hot sun (90* temps) last for four days--in fact there was a lot of ice still left when I got home, probably enough for another two days. The food stayed nice and cold. The car will smell of food anyway, even if the food isn't inside. Unless you're going to Yosemite, where bears do break into cars, you may be over-thinking the issue. Of course, in the California parks, the car-camping campgrounds have bear boxes, so even there you need a bear-resistant container only for backpacking.