The most common number, IMHO, is 20 rounds or a little less. The reason is that a standard box of ammo is 20 rounds, so it is an easy packet to carry. Often is is a little less because a few rounds have been fired to sight in the gun, or during a previous deer season.
I always liked to carry a box of ammo because there are times when you need more than just two or three rounds. You may shoot at a running deer and expend several rounds, you might want to head shoot a rabbit for camp meat, you may have an opportunity to shoot a porcupine that has been chewing up your hunting shack, someone else may have only brought a couple of rounds and needs to borrow a couple, etc.
Many seasons, though, I have not shot a single round or only one or two. Some people just load up their rifle and not carry any extra rounds.
Thanks...I was just curious. Our guys shoot on a couple of privately owned properties so I thought thier amount of ammo carried may differ. My daughters boyfriend is always running hunters off his land and out of thier tree stands, so I worry even more now.