It is not widely known but, Starbucks does provide “for here” mugs and plates if you ask for them when ordering.
One can speculate why baristas are not instructed to offer a mug with every hot beverage ordered, I mean, every other fast food joint asks “is that for here or to go?” I can only assume it is cheaper to avoid both the cost to replace breakable mugs and dishwashing.
So, next time you sit-in at Starbucks, and you are not carrying your personal travel mug for some odd reason, ask for a mug when ordering your latte. Next time you just cannot say no to that chocolate croissant or that spinach wrap, it happens to the best of us, ask for a plate. I do, however, regret to inform you that all of the goodies in that tantalizing display case are individually wrapped in plastic!