In Wisconsin, if you can show that you had a reasonable expectiation that you were in danger of losing your life or incurring grave bodily harm, you can justify drawing your weapon and using it if need be. Every case is a little different depending on the relative abilities of the attacker and the victim. But you can't draw to only protect your property - human life is valued more than someone's wallet - if there is no clear indication that the attacker was going to hurt you. Unfortunatley you can't just guess - you have to be able to point to a reason that you felt your life was in danger - somehow the person has to actually threaten in some manner that could be considered deadly force that can be met with deadily force. If you pull a gun and can't show that you were in danger, YOU are the one threatening deadliy force and can be considered to be performing the criminal act.
I carry two wallets, the bigger one with money and some junk stuff of no value, the smaller and less obvious with the credit cards, drivers license (CC license!), etc. I also carry some pepper spray that I can pull out easily if someone asks for the wallet. The gun stays put. if I did pull it out I would hope that the person would have enough sense to give it up and back off. I would not immediately shoot unless it was obvious that the person was in the act of attacking me and was not going to stop.
However reality is messy so who knows what would happen. Just don't go looking for trouble in the first place. Use your head and think before going places where hindsight would tell you that being there wasn't too bright.