Use one for what, hunting? More and more often I find myself going out with only my gun or bow, and what will fit in my jacket pockets. To heck with all that other stuff!
For longer hunts I use a fanny pack, unless additional clothing is needed - then a backpack. If I'm not sitting all day, I get by with my cargo pants, and HSS vest pockets.
I tend to use a fanny pack during archery season and then a large backpack when I hunt from my tower blind as those tend to be all day sits and I tend to have one of the kids with me as well. I try to keep gadgets to a minimum and that really helps cut down on the "stuff" you need room for.
I use a small backpack. I hunt from a homemade saddle instead of a stand, and the saddle goes in the pack until I get to the tree. And my linesman spurs go on the outside.
I hang the linesman spurs until it's time to come back down, so the pack is almost completely empty when I'm in the tree. Just a knife, a few trash bags for quartering, a couple pens, snacks and water.