Until like five minutes ago I was absolutely 100% sure the coffee cup was a lucky charm.
When we see Marinette unifying the two miraculous, she's already in her luckycharm suit. And in the next scene, Marinette is holding a seemingly useless object. Obvious conclusion: lucky charm.
Marinette was as I assumed stuck in the bubble. She couldn't have gone out to get coffee. I thought the only source for it could be a lucky charm.
I don't how I failed to notice the coffee cup isn't red. I'm so stupid. The idea that it's not a lucky charm just never occurred to me.