I've settled on a similar system to several of the posters, though maybe a bit more costly than some.  Last year I purchased a poly food box from BWJ ($105).  At about 3600 cu.in., it fits nicely inside a GG Superior (or whatever it is called), with room for a few other items, like cutting board and a tarp.

The box adds some weight to the system, but it corrals everything nicely, has a frigerator-type gasket on top and a good closure system for the top.  Will easily carry two weeks worth of food for two.  Can be used with or without foam insulation.  I used an old piece of ensolite on a fall trip last year, and everything stayed nice and cool.

Since I am a hider, the box is mostly critter proof, though certainly not bear proof, and I wrap it up tight in a tarp, with an alarm system perched on the top.  Have had no problems so far, knock on wood.

With improvements in kitchen containers, I use more semi-hard-sided Glad-type units and fewer plastic bags than previously.  As others noted, crackers, and in my case fresh veggies, really carry well in these.

I experimented with carrying a couple of water filled and frozen 20 oz. gatorade bottles last fall, thinking maybe we could have ice in our evening cocktails for a few days.  It worked, but paddled/carried 40 oz of ice about 20 miles.  Not sure if it was worth it...