Revealing mistake: Near the end, when Morgan Spurlock says "Why not do away with your Super Size options?" the water condensation runs UP the drink. (01:34:00)
Factual error: Morgan says that french fries are one of the seven items on McDonalds menu that doesn't contain sugar. French fries, in fact, do contain dextrose - a form of sugar. This is mentioned on DVD commentary.
Chosen answer: If you were going to eat at McDonald's three meals a day for 30 days, would you actually make 90 separate trips to the restaurant? I'm sure there were times that he got 2 or 3 (or more) meals at the same time and simply reheated them. As for the cups, I know lots of people with old soda cups on their desk and tons of them in their car. The crew may have had food too.
Myridon