I use multiple methods depending on situations....

I have a giant cooler in my trunk with soft cloths at the bottom. If I have to leave my camera equipment in my car for few hours, that's where it goes. I know, even in Florida, it's perfectly safe for few hours. There is NO ice in it, by the way....

If I'm *just* carrying a camera body and a lens, I either carry it on my shoulder exposed if it's going to be an active shooting day, or put it in a single camera case if I feel the need to protect it. If I have multiple "stuff", I might choose to use my small camera bag with 3 slots or a backpack. I have a giant multi-camera camera-bag but I never use it. It's too big, too heavy, and I don't have an assistant.

Cooler is a pretty good choice. It's rugged, cheap, and no one suspects there are expensive stuff in it.

One day, I was carrying my F100 with a pair of f/2.8 pro lenses in a public park. A lady walked up to me and asked, how much would something like that cost? She was well dressed and courteous but it made me nervous. I said, "oh, it's a film camera... it's worth nothing." I left that area quickly.