I have hunted the often vertical hunting fields around Tucson for 20 years. I have used many options: No pack, small fanny packs, big fanny packs with and without shoulder straps, small frameless day packs that were inexpensive but solid and well made.
For hunting out here on warmer days I carry::
1. A rifle (or bow) slung to the KIFARU belt with their rifle carrier. I sling the rifle under my arm when I am hunting for quick access. and behind my shoulder on the pack frame when packing out. I can still access it from either place if needed while walking.
2. 1 or 2 2/3 liter hydration bladders, depending on how far from the truck I get.
3. Spotting scope/large binos and tripod in pack or on frame
4, Small binos, radio, range finder, kestrel, phone, in-reach, Garmin GPS, all in molle pouches on a chest rig. I use a modified military surplus load bearing vest for my chest rig. I always wear the chest rig with or without a day pack. This is the heaviest thing that is load bearing on my shoulders. My day pack options carry load on the belt, not the shoulder straps.
4. Kill kit, food, first aid kit, extra ammo, rain gear, flash light, etc. in the pack.
What I have come to find works the best for me is:
1. A KIFARU Duplex Lite Frame or K4 FRAME on a KIFARU belt, with an appropriate size KUIU pack, usually about 3600 to 4500 but sometimes as small as 1850. All the bags compress down to the frame if not full. The KUIU 4500 Divide on a K4 frame with a KIFARU belt is my ultimate idea for a day pack, but I don't own a KUIU 4500 Divide pack yet. I won't pay full price and haven't found a used one yet. A straight up KUIU frame pack will do well for a light day pack too, but it is not great when loading out meat. It is serviceable, but not great under heavy load. I prefer something with a KIFARU belt, because it will carry the weight of my rifle all day, and there is nothing better for load bearing comfort than a KIFARU belt.
2. Another alternative is to carry a KIFARU or K4 frame with a KIFARU Cargo Panel with various military surplus molle pouches for my gear. This option is a great very light weight option that is very versatile, and can be done for under $400 if you buy everything used here or on fleabay. People are ditching their Duplex frames for the new ARK frames.
3. With either option I carry meat bags and/or a large roll top bag compressed between the pack and the frame, or between the cargo panel and the frame for packing out meat and/or as a stuff bag for layers or apparel shed in the afternoon heat or for rain gear when needed.
4. Remote antenna for radio attached to pack frame, or back of bino chest rig.
5. If I am hunting within a mile or so of the truck and only going to be out a few hours and come back to the truck at lunchtime, I sometimes just carry my chest rig, and a KIFARU pack belt with 3 military fanny packs on the KIFARU belt. One on each side and one across the back. (I am a big guy and wear a large belt, so this works well) These military fanny packs have built in molle attachments, full double zipper closure that will open from either end, and compression straps that keep the bags low profile tight to the belt when empty. They are well made and durable. 2 - 3 liter hydration bladders will fit in one fanny pack. I buy these military surplus fanny packs 10 at the time for about 4-5 dollars each on fleabay. I keep a lot of my gear (first aid kit, kill kit, meat bags, rain gear, hydration bladders, etc.) labeled in these full double zipper pouches, then just attach them to my KIFARU belt, or my Cargo Panel, or pitch them into my KUIU frame day pack as needed. They are kind of the base unit of my packing system.