I am with Jimss. I have hiked all over AZ in warm and cold weather, with no pack, small fanny pack, large fanny pack with and without shoulder straps. and for many years decided on a small frameless pack. and rifle on a sling. I am always back at the truck by nightfall, and usually by lunchtime. The fanny packs were fine for gear, I go lite, but I usually have to shed a coat by mid morning, and the fanny packs were not great for strapping a jacket to. The small frameless pack was fine for my gear and better for strapping my jacket to, but it just got tiring pretty fast in the vertical terrain where we hunt. My rifle was always sliding off my shoulder, especially when there was a pack strap under the sling. I had the same experience as Jimss, shore shoulders, sore back, a lot of fatigue by the end of the hike, even a half day hike in rough terrain. I really like the KUIU frame packs and bought an 1850 for my first frame day pack, but that was too small. I like the KUIU packs because they match my camo, and when the deer can see you from miles away, blending in is VERY important. They can still see you when you move, but lose you when you stop. I also like that their frame packs have a huge 3 sided horseshoe zipper that make finding things in the pack simple. They have the accessibility of a fanny pack with a LOT more room.
KUIU packs are great for organization, and their belt, straps and frame are comfortable for light loads, much more comfortable than a frameless pack, but as weight increases, comfort decreases. Although they are designed to put meat between the frame and pack. if you do that, it is going to FEEL like a LONG hike out, even if the distance is short. KUIU weakness is their lack of belt comfort under heavy load, and belt to frame connection that allows heavy loads to sway as you walk. NO BUENO. KIFARU belt, frame, and straps are great, regardless of weight.
If I was going from scratch today for a day pack. I would go with a KUIU 4500 Divide pack, on a KIFARU Duplex Lite frame. with a KIFARU Gun Bearer for the rifle, with a MILSURP rolltop dry bay between the frame and the pack, empty for a pack out if needed (keeps blood off me, my clothes and my pack.) I would carry another dry bay in the pack with a bivvy and dry clothes if the weather is rainy.