I use a Bearikade Weekender. I've never pushed the limits, but for solo trips I've had up to 6 days' worth of food in there. I've never felt the need to hike longer than that, but if I did, I'm sure more would fit with proper meal planning and packing. I can usually fit my cookware in there as well as food.

I've also had 3 days' worth of food in there when hiking with my wife, and 2 days' worth for 3 people. There's always food left over, maybe a meal's worth. I've never tried to cram it full.

I think bear can manufacturers & park services have already done some equations to figure out food capacity in terms of volume and # of days per person. I think they're based on "typical" food choices for hikers, though; the average person isn't going to try to get the most bang per ounce or cubic inch. It would be interesting to see how the lightweight crowd fares.