Just watch the prices. Most are rip-offs. I bought a "Badlands" day deer pack a few years back. It was almost $150 IIRC and it was complete crap! Whatever you do, I recommend you hold it in your hands, open all the zippers(using only your weak hand), and make sure it is what you need. I know you're an experienced hunter and all, I say this more for anyone else reading this.
Yeah, I used that POS for the last 5 years(to get my monies worth) but I'm finally dumping it this season.
How much do you need? I went with a surplus MOLLE butt pack in woodland camo my first year and it fit a harness drag, first aid kit, snacks, inflatable pad for sitting, a couple of canteens on the belt, my knife and a few other small items. The next year I got a new one in Multicam to go with my new Multicam ACUs. Part way through the season I picked up a Midway Rendezvous pack. https://www.midwayusa.com/product/939300700/midwayusa-rendezvous-backpack Looks like they only have it in OD and black right now, but they had them in Realtree Xtra last year. Great little pack. Has an OD rain cover included. Perfect size for being put all day, plus extra clothes.
I still prefer a butt pack when going light, especially if I plan to still hunt. But the small backpack can fit everything from the buttpack in or on it, plus packable rain jacket and pants, ACU jacket, hat and gloves and a good book to read.
I tend to try to go out to the field stripped down and then layer on once I've cooled off. In really cold weather I lash my parka and/or bibs (I picked up a set or Herters stuff on clearance right at Christmas last year for something like $120 for both after clearance, sale and discounted gift cards) on the outside of the backpack with a bit of 550. Easy to attach. The backpack also fits great under the climber stand I just picked up. Adds a comfortable layer of padding.
Not a setup that would work if you were packing the animal out, but great if you are dragging or using a cart.