Hello DV,
The best pack for light weight mountain hunting is dependent upon a number of different variables. You could help us all out by giving us a few parameters related to the nature of your entry into the area where you will begin packing. Secondly, this will also include variables based upon the number of days you expect to spend hunting. Thirdly, it would be useful to know which animals you are hunting so that not only volumetric considerations are given for our opinions. While I have a number of different backpacks they are each best suited to a different application. If you want a purely, "One pack for everything," that'll winnow down the number of packs available to you. New technology is opening up a host of options to achieve that objective.
I use a Barney's Sports Chalet for long hunts without regard to species, for moose hunts without regard to length/packing distance, or for winter hunting without considering ANY other pack.
For my light weight option I am currently running a Stone glacier Sky Talus. There are a number of packs similar enough to this design concept that comfort and expandability are not exclusive to this manufacturer. Try on a bunch of them to see what works the best for you. Shared up your experience so we know which options were most attractive.
Cheers!