I'm just going to say that when you work at a fast food place- even a make-to-order place like Taco Bell that you tend to make food automatically. It's not uncommon, if you listen to the Taco Bell food makers, for the person who starts the order and communicates what's on it to say things like "these tacos are no lettuce. No lettuce! No- Okay, THESE tacos are NO LETTUCE. No Lettuce." and so on. When you're really tired and on auto-pilot and keep goofing up the first person might just make that meal him/herself.
Yes, I am talking form experience.
That said, the Taco Bell closest to me tends to do the random food handout trick at the drive-through, where you get home and random extra food has been stuffed in your bag. I went throught it with my sister many times (I don't really do Taco Bell any more) and while she always got what she ordered, she also always got extra random food as well. We always used to wonder how many people came back mad because they were missing food.
I don't like the McDonald's near me much unless I want some place quiet to surf the web as food takes forever and the help seems to be rather lackadaisical for a McDonald's.