How would you avoid theft while being around a populated campsite?

I agree that it is best to leave any unnecessary valuables at home, or at least lock in a spot in the car where they are not visible. I have not actually ever camped in a place where I was concerned about having anything stolen; but usually the only thing that I had to be concerned with would have been my car keys and billfold, which are easy to tuck into a backpack or one of those small crossbody shoulder bags. I use one of those instead of a purse most of the time anyway. It is small, lightweight, and I can be slung over your shoulder (which is why they are called a sling bag, I guess), or you can wear it as a crossbody bag either on your back or your chest.

 

I consider the campsite like a neighborhood particularly the big campsites that can accommodate many camper groups. You should not leave anything valuable in your tent with no guard. That is the way we do when I was a boy scout that we assign 2 scouts to take charge of tge camp. We call them quater masters. When we have an activity away from the tent, the quarter masters stay in the tent area.