Don't get too hung up on packs, Eberlestock packs are popular, I've used three of them over the years, in addition to Eagle 3 day packs, Camelback packs, even an old ALICE pack. The key thing is that it doesn't have to be huge because chances are you're going to want to fill that thing up. About 2,000 cubic inches is ideal for me since it's enough room to fit the gear I want with some extra room left over for snivel or rain gear. Side compression straps are nice since it allows you to strap tripods or other gear to the side. This is one thing I hate about my Eberlestock Gunslinger II, too many freaking straps but the internal organization is amazing so I keep it around.
As a baseline I pack the following
Mags
Ammo
TAB Rear Bag
Armageddon Gear Game Changer
Armageddon Gear Fat Bag
Homemade dope older
Painter's tape (rolled around 1/2" PVS pipe with cord run through and taped to Sharpie)
Sharpie
Kestrel 5700
Leica LRF
First Aid Kit
Multitool
Otis Cleaning Kit
Armageddon Gear sling
Knee pad
Sunscreen
Ear pro
Eye pro
Optional/Match Dependent (This stuff will usually ride in the vehicle)
Tripod
Shooting Saddle
QD Tripod Mount
Convenience Bag (2 one gallon zip locks, Dry Hands, foamy ear plugs, zip ties, duct tape, 10' 550 cord, hand wipes)
I only pack wet weather gear if it's calling for rain or if it looks like it's going to be muddy and I remember to pack them. I don't typically pack extra clothes but I have taken extra clothes but kept them in the vehicle for later, extra shoes too. Food, water, snacks that stuff is up to you, generally I'll take a couple bottles of water and some Clif bars and do ok for the whole day.