This is something I've been working on for a few weeks. I always preferred a shoulder bag for hunting, rather than a waist pack or daysack.
The main body of the bag & front pocket are made from 2.5mm veg tan, dyed deep brown & well oiled. I sewed in a 4" gusset of 1mm leather to allow plenty of room inside. The front pocket has a 1-1/2" gusset. To prevent it all just falling open, I bolted in a retainer that hooks on a piece of Moose antler, under the flap. The pocket is closed with a sam browne stud.
The strap is 2" wide, 3.5mm belt strap, tapered to fit a 1-1/2" oval brass buckle. The bag is suspended on 2" brass rings, which I can use as tie-on points for any extras I may want to carry (I often take a small wool blanket)
The strap & all fittngs are attatched with Manchester screws so I can easily repair or replace any of it in the field (I built this with a looong future in mind!)
The bag is 13" tall, by 11" wide, giving me plenty of room to carry supplies for a couple of day at least. I'll be giving it a good week-long workout in South Texas next month