I totally agree with this suggestion. If you need to haul some things a long way, a cart would be superior to carrying it on your back. It's not like you need to navigate trails or anything. I made the same suggestion in this post a while back.

The added benefit of the cart idea in NYC is, as bws48 points out, they are already a familiar sight that doesn't attract much attention. Well, if you were pushing one in a business suit across the Brookly Bridge, that might seem odd, but otherwise, I doubt it'll get much notice. In this summer heat and humidity, just being able to carry a decent supply of (heavy) water with you on your trek home would be a big help. Sure, you may be able to buy bottled water from a deli or bodega on the way home, but maybe they'll already be sold out because of the thousands of other thirsty people hoofing it home, or maybe there will be price gouging or maybe they'll just be closed.