Some swear by them, some don't. This is kind of a tough question to answer because there are so many different styles of hunting, individual's physical limitations, nationwide terrain differences, etc.

My 'basic' day affield: bow, release, grunt tube (depending on time of year), flashlight, proper clothing, knife, multi tool, compact cheapo binocs, handkerchief for who knows what, and maybe a few other things. Sometimes, I will carry hand pruners, Gerber exchange a blade saw, rangefinder, or handwarmers. Generally speaking, if it doesn't fit in my pockets, on my belt, or around my neck I don't take it. I'm not a fan of a separate gear bag.