Yes, I understand your consternation. 50 years ago I made the switch from a full framed pack (an older 7pound Korean War military surplus pack.) I switched to an internal framed Tough Traveler (3500ci, 34oz.) But I lost my pockets, pouches, and, my organization. I used it for over two years before I became comfortable organizing it. I agree with Roger, with a single compartment, organizing things so they stay handy can be a trying task.
Today, I use mostly a Murmur(2012 version) at 2200ci or a much newer HMG SouthWest 2400 (approximate ci,) 2018 version with small hipbelt pockets. Anyway, I organize my gear first by water resistance, second by use. I also do about half my trips with a canoe and sometimes in rain storms, so, water resistance is rather crucial if I happen to flip the boat (rare, but sometimes getting in and out can be difficult.)
This is done by simply separating your gear into two piles.
For example.
1) My dry gear is usually food, sleeping bag, long johns, down jacket, socks.
The first sack loaded (and last needed) is my sleeping bag and long johns, socks, down jacket. This contains everything needed to stay warm and dry. (Sometimes I am wearing my jacket, but I have a wool sweater/fleece I wear while hiking. I rarely need anything while hiking, though. Usually, just a synthetic hiking shirt (long sleeved) keeps me warm enough down to around 40F/5C. Lower, and I just bring the appropriate clothing.) With my rain jacket over a loose sweater, I’m good to about 25-30F when moving. Anyway, this gets put into an eVent compression/dry bag, squeezed down to fit into my pack length wise. This is then loaded into the bottom of my pack.
The second dry item is my food. I put my food into a standard dry bag (doubles as a bear bag) after taking out my snacks/lunch and slipping this into a plastic bag. This is then loaded into my pack. Sometimes I carry two, 13L drybags for food for 2-3 weeks. T
his covers my crucial dry gear and takes me down to around 10F at night for early spring and late fall trips.
2) The other 1/2 to 2/3 of my gear gets put into my ditty bag (doubles as a rock sack for tossing the bear line up) and stuffed into my front/side pouches. Head lamp, bear line, spare line, a spare set of batteries, phone, TP, superglue, hair brush/duct tape, fishing gear (hooks & sinkers, flies, float bubble, small 40″ collapsible rod, stakes, wallet, stove, etc. This is a stout nylon 1L bag, not a dry bag. None of this stuff really cares if it gets damp. Batteries are not a worry, and the phone is ruggedized/waterproof to about a meter of submergence (as are my lights.)
My tarp rolls up small enough to fit into a 1qt grease pot. This protects the tarp and protects the pot against bending…it is also silent while hiking. The ditty bag and grease pot goes into my pack with my NeoAir pad. This completes the main body.
Front pouch carries my 2L Platty (empty,) my steripen, rain gear, fishing reel, maps, lunch, plastic garbage bag(usually a 1qt ziplock,) polycro ground sheet, and sometimes a sweater. I can access these easily from the outside.
One side pouch is for two 1/2L water bottles. The other has my fuel can(s), windscreen and trail saw (often needed for clearing trails.)
My hip-belt pockets have drink mixes (usually just flavoring to kill tannic water taste) and bug dope.
I have my pocket knife, bug dope and afterbite/benydril in my pockets. Sometimes I will carry the steripen there, too. My compass is around my neck along with a car key.
I can usually hike (or paddle) the whole day without needing to open my pack for anything. I am good to about 20F without worrying about getting anything wet that is really important. The HMG is fairly water proof and the Murmur is OK in a rainstorm. In a pinch, I can put my spare socks (usually drying on my pack front pouch) on as mittens. I only need three bags: dry bag for food, eVent bag for cloths, and the ditty bag.
Anyway, this is how I organize stuff in my pack. You might need another bag for your cook kit if you use a wood stove, or maybe a liquid fuel stove…