I don't actually go to Starbucks, but at other smaller coffee shops, I will occasionally tip. Not always. Sometimes $1, or sometimes just the change will go in the jar. I suppose I should, but baristas aren't considered "tipped" employees and they're paid more than the little $3/hr that servers are. If I order food too and I go sit at a table and they bring me food and coffee, then yes, I'd tip under those circumstances.
Fast food like Subway or even faster food like McDonalds - nope. I never tip for a carry-out either, like pizza or picking up from a restaurant. I figure, the tip is for service they give when I'm there, filling my water, refilling my drink, bringing my food, making sure it's all taken care of. If they literally pick up a box from the kitchen and hand it to me, I don't see why a tip is necessary. It took them maybe 60 seconds. I do tip delivery people.