Apparently there is a law of physics that states that any discussion of pistols has to morph into a discussion of stopping charging bears.
I used to carry a S&W model 12 for the exact purpose the OP proposes. I eventually decided that:
1) The chances I'd need it to finish off a deer were pretty small.
2) It was more trouble than it was worth to lug even a light pistol and ammo around along with the attendant bother of locking, storing and transporting it legally, not to mention the complications of carrying it during hunting season.
3) If I ever did need to administer a coup de grâce, I'd just do it with my rifle.