someone at the restaurant bags the food correctly, includes all the napkins, utensils, sauces, etc.,
But every job requires some kind of job duty. When I was a cashier in a drugstore, I had to ring up the sales correctly, be polite and friendly to customers no matter how they treated me, put the items in a bag, etc etc. Nobody tipped me, nor did I expect them to. It was what I was hired to do. And while I realize that in some places, servers get less than minimum wage, that is not the case here and we still have to tip them.
In a sense, I agree with this. To my mind, it's the job of the servers to serve food in a pleasant and professional manner. If one does so, why should they be tipped? Tipping should be saved for something extraordinary. At least, that's one way to think of it, and if I followed that, I would almost never tip, and in my culture I would then be in the minority, and people might even feel I was being rude. I think this is one reason why tipping threads can become so heated--on the one hand people say, "We shouldn't have to tip people for doing their jobs," and on the other hand people say, "But they don't actually get paid fully by the restaurant for doing their jobs, it's assumed customers will tip them." And of course the payment structure varies significantly by the restaurant, industry, and even geographic location within the same country, let alone other countries.
I think, if there is a general culture of tipping, but you aren't sure about a specific instance, giving a small tip would err on the side of caution, especially in the moment. In a larger sense, it helps me to think about what duties I would be tipping for, if I tipped.
For example, one casual restaurant I go to has a tip jar on the counter. You order at the counter, pick your food up at the counter, and clear your own table at the end (though it's not fast food like McDonald's). I thought, what extra labor, besides taking my order and making it correctly, and general cleaning and maintenance of the restaurant, are the employees doing for me, that I should tip them? (Asked seriously, not in a snarky way.) I couldn't think of any, so I've decided not to tip when I eat there. (Besides which, the tip would occur almost before they'd done anything for me at all--so how would I even know if the service was worth it?)
Previously, I never tipped on carry-out because I didn't think much work went into it, but those here who've worked in food service described some work that can occur in some instances, which I'd never thought about. Now, I usually tip a small amount for carry-out (unless as I said it's just one small item). That's just what I choose to do, because I prefer to err on the side of caution, and I have neither the resources nor the interest to figure out the payment structure of each restaurant I eat at so I could tailor my response to each. Other people have different ways of doing things--to me that's the issue at the heart of tipping, because it's almost entirely voluntary (except for "parties of 10 or more will be automatically charged 20% gratuity" and other such restaurant policies). Personally I think it's interesting to know what thought processes other people go through when making their decisions.