Oh the joys! I have experienced this everywhere! If he has not begun going crazy, but is being calm, and not posing a threat to himself or others (kicking, in the middle of a street, etc.) Be gentle, and calm with him. I've sat down in the middle of a crowded store with my child. Just sat there with him. I've stood patiently in the middle of the street with him (on our street, we live in a rural neighborhood so wasn't a danger). He's overwhelmed and exhausted, most likely. You're describing places that are hectic and fully of sensory overloading stimuli.

You can let him know you understand how he feels, but maybe we can move someplace a little safer and quieter. "Wanna go sit in the car with me and unwind?" I know it seems patronizing, but when he's not having a full blown meltdown, sometimes I just have to let him get it out.

I also tend to use transportation things in places I know he'll become too stimulated. I go for the car shopping carts at the grocery store/home depot or the large seated carts at Walmart. I bring a Red Flyer to get him from the bus stop (not to take him to, as he is fine in the AM) or when we go to the mall. He's 7. But, I do understand he's struggling and exhausted and overloaded, so I do accommodate him during these times. It also helps keep him from running away or wandering, as he does these things when he gets too much going on around him.

Before they had the big seated carts at Walmart, I've even bring a pillow and blanket with me and put him in the cart. :P Some may see this as a negative thing, but it works for me and him... and I can do what I need to do with much less stress.