Food is differnt for different people and metabolisms. Different weather conditions call for different ammounts. Hiking peaks calls for more than hiking flatter trails. Paddling has different requirements. Age generally means less food required. And so on.
Food density is very different. A simplistic example: Fresh Apple vs Dehydrated Apple. Simply shifting to all dried foods will take a 3 pound per day requirement down by 40%. Many vitamins, sometimes minerals are lost, though. Adding back 7 vitamin pills is still a lot lighter.
Cooking as opposed to prepackaged meals. Maltose, sucrose and salt with low density carbohydrates and some protiens. They lack fats and are generally only about 100C/oz. 2 cups of cocoa/oatmeal, 2 cups of coffee, for breakfast. A couple chocolate bars or other food bar, maybe a handfull of snack chips, for lunch stops. Fried dough, a soup/stew or rice dish, a cup of cocoa at night is a typical meal for supper.
Fats are the big key: Fritoes or other snack food are good for 160C/oz. Chocolate is about 135C/oz. Nuts average about 170C/oz. Jerky is only about 80C but goes a long way. Pepperoni(120C/oz,) salami(130C/oz,) cheese(110C/oz,) dried sausage(110C/oz) are good protiens to carry and have a lot of calories. Olive oil, parafied butter are usually carried in a couple 4oz bottles(250C/oz.)
I usually plan on 3000C/day in warm weather (>40F average,) so, my food weight is about 18oz per day or around 1.1 pounds per day. Typically, for two weeks out (14 days) my food weight is about 15-16 pounds. During shoulder seasons, I plan on 4000C/day and food weight is around 1.5pounds per day or for a week out it is around 10-11 pounds.
Maximimum weight I can get into my little frameless is ~25 pounds. I use a Gossamer Gear Murmur in summer and typically carry 22-23 pounds for a maximum duration of two weeks. For the shoulder seasons (now) my maximum pack load is 30pounds using a Gossamer Gear MiniPosa (forrunner of the Gorilla.) I usually carry 27-28 pounds for a two week trip. But, I am older and retired. I don't need or want that much food when I am out.
Frameless packs were initially difficult to carry. I went back to an internal framed pack. Examinig a G4 pack, I noticed the pad keepers. So, I got a Gossamer Gear G5 and a 3/4 length NightLite pad. I cut this and taped it together into a thick "frame", it *just* fit into the older G5-spinnaker. But, it also became the best internal framed pack I had. Adding this to the Miniposa, and Murmur were no brainers.
The problem with pads inside a pack was they tended to slip up. After a few hours, I noticed the bottom 1/4 of the pack was floppy, my hip belt was loose, and my shoulders were getting sore. With the external pockets, the pad stays put very well.
With the Murmur, I chopped it down to three layers. It works fine for anything up to 25 pounds with next to no pack collapse, the primary cause of sore shoulders. I still use the old 5 layer pad in the MiniPosa...even after switching to a NeoAir a couple years later (when they first came out.) I added them to other packs as well, I am sure you can add them to most frameless packs. Though, Gossamer Gear dropped the 3/4 lenght pads. You can use multiple SitLite pads or get another from Nunatak as the Luna pad. The "bumps" lock together better than a plain pad for a 1" support for every two layers.
Anyway, I use small volume packs (Murmur-2200ci, Miniposa-3000ci) with a fairly stiff suspension. Hip belts are needed. I have neck/shoulder problems from a 30 year old construction injury and cannot puy more than 15-20 pounds on my shoulders for any length of time. I *need* the weight on my hips. Sounds like you do, too. The shoulder harness (shoulder straps and torso strap) only supplies stability and maybe 5-10 pounds of weight handling. I can usually put my hands under the straps anytime I am hiking by simply shifting my shoulders. The penalty for this is the weight of the pad used for the suspension. It weighs about 8oz. But, I often use it to level a sleeping area and to prop up my torso/head for sleeping...simply open up one leaf on the three layer pad...even using the NeoAir.
As I mentioned, pack collapse is usually the biggest cause of sore shoulders. Not using a hip belt is the next biggest one. Both are directly related pack suspension. There have been several articals written about that, here, over the years.
The other thing is lack of exercising those "carry" muscles in your shoulders. I carry a 45-50pound exercise pack around most mornings (with a wide hip belt, of course.) So, I don't notice it when I head out. If you only pick up a pack a few times a year for hiking, your shoulders will get sore, even with only 10 pounds on them.
Anyway, I hike mostly in the ADK's, so water isn't really a problem. I carry two .5L bottles(about 2 pounds.) I only treat water I will be drinking. Cooking boils everything else. Desert hiking is different. Dehydrating food doesn't even make sense. You need the water.