I've seen wallets, purses, bags of groceries, jugs of milk and once a very committed cat going for a ride on the roof of a car. These all have a proper place to be while enjoying the scenery. A gun should be in a holster, in his hand or stuffed in his tighty whiteys so that he KNOWS where it is at all times.
That said, I once proudly open carried for 6 hours before noticing I had an empty holster! :what: Once my heart started beating again, I mentally back tracked and realized that I had never actually touched my gun that morning and it was still sitting at home. Doh!