If I can, I pull up as close to the door as possible then unload the amp and cable bags, then come back and get the upright, then park. Loading out is the reverse: bass first, then amp/bags. My logic is if someone is going to try to steal something, it'll be harder to get the bass out of the car than it is to grab a bag and run.
If I can't do that, I use a cart.
Sound thinking. Years ago when I was younger and dumber, I stopped at a taqueria after a gig. I came back to a broken window and someone zooming off with my amp, cab, and other cables and accessories. The bass was right where I left it; they didn't know what to do with it or how to get it in their car. It's still my main player today. I'm glad it was spared.