In the bar M. Jo puts down a bottle of champagne on the table. It's almost completely full. Luigi then picks it up, while it's still full. However, when he stands up and threatens M. Jo with it, it's empty.
The goof items below may give away important plot points.
After Mario, the lone survivor, delivers the explosives, he heads back to town. He crosses the pool of oil on the road very fast, splashing oil on the workers and smearing the truck. A little later, we see a clean truck without a hint of oil or even mud on it. No car wash in between, though.