transactional services = no tip
counter service (where they clean up a mess I leave) = 10% tip
to go at a full service restaurant = 15%
Full service restaurant = 20%
There's a donut place around here that we visit often (2-3 times a month). We go during their busiest weekend hours (mornings before 11 a.m.) and they are always putting out hot donuts at this time.
The counter service will ask you if you want them to go back to the fryer and get you a hot dozen. IMHO, that's above-and-beyond service and I will give them a 15% tip for that. And also because I go so often and want to be remembered fondly.
Same donut shop during king cake season: They'll put out 10-15 ready-to-go king cakes under the counter. I go in and ask for one, they hand it to me from under the counter, two seconds flat. I might thrown on an extra buck or two, but just as often I don't.