It depends on how long that I will be hunting, the game, and of course, the gun. Typically, I would say that I have whatever firearm that is in my hands fully stoked-whether bolt, semi, lever, etc. for fast follow-up shots-should they be needed. There is typically then 5-10 additional cartridges on my persons with another 20 or so accessible in my truck or the cabin, as needed.
The reality though is that I have never had to dig into a second pack or box of rifle ammunition while hunting and safely return the majority back to the ammo cabinet upon my return home.
Now shotgunning for birds is another story...

Back the truck up and get that liftgate down!