[mindslight]

A sandwich shop is selling you an item for a price. Handing you the item you bought isn't rendering a service, and so there's nothing to tip for.

The idea of tips as feedback is fallacious - a server doesn't know if a 15% vs 20% tip is due to their performance or just the person tipping. And the service has to be really bad to leave no tip at all (and even then, there are plenty of people who do this regardless of service). Furthermore, especially with a to go order, customers won't even see their orders until they get to where they're going and unpack. The real incentive/feedback in the restaurant industry is whether customers come back.

The answer to the larger topic is just say no to attempts to expand the terrible practice - the original Uber had it right. And stop making excuses for not paying attention to dark patterned UIs, like being perpetually "in a rush" or worried about the people behind you in line. Take some responsibility for knowing how much your order should cost, so you notice when the big number disagrees.