I believe that if you have a large order, or something that will take a great deal of time, that it is courteous to let a person behind you go ahead. I usually have a cartful of groceries, so if there is a person behind me with a few things I let them go ahead.
There is a fast food sub shop where, for each sub you order, you tell them your choices for : the bread, the meat, the cheese, the veggies, and the dressings, as they make the sub. If you order 3 subs, you go through this 3 separate times. It's fine under normal circumstances. However, one day I went in and a mother and her teenage son walked through the door one step ahead of me. They were ordering about 20 subs, they each had a paper with a list on it. I couldn't believe that this woman was so clueless as to let me stand there while she and her went through the process of ordering 20 different, individually prepared subs. She wasn't required to let me go ahead, but any reasonably considerate person would have.
And I know that most fast food restaurants prefer you to phone ahead with a very large order because it can be disruptive to their normal service.
Yeah, I think it would have been considerate for the doughnut guy to speed it up a bit.