I have made the change from wearing a vest myself, for both hunting and fly fishing. For some reason, if I wear a vest and carry any amount of gear (i.e. weight) in the front of it I end up getting upper back fatigue/pain after an hour or two. It's been like that my whole life. If I wear a bag at my side strapped across one shoulder/chest I don't have that problem.
Years ago I made a switch to nice Brady Brothers bags for my fly fishing tackle, and couldn't be happier. For hunting, I generally hunt with muzzleloading guns now, so I wear a shooting bag with a clip on game carrier strap for carrying birds.
For the type of bag you want, check out Brady Brothers
http://www.bradybags.co.uk/I think they have the style you are looking for. They are somewhat pricey, but the quality is second to none.
