I just went through this a couple of months ago, your assessors will judge a lot by how you can tell a story and how you use Starbucks lingo. Use as many examples for your answers as you can and use the words support, recognize, include etc. Don't be afraid to ask them to rephrase a question if you don't understand what they are asking. Your coffee tasting won't be a huge part of the assessment but it's a good way to show your personality and warm up to your assessors. Don't wait for them to start, if you're supposed to be starting at 2 then at 2 go ahead and make sure everyone is ready and begin. Come up with some questions to ask them as well.
For the in store part ask the shifts if you can run the floor and be aware of how they run their shifts/complete tasks. You've already been chosen to lead so you show the characteristics your store manager looks for in shifts now you just need to get a rythym. Don't expect perfection at first, a lot of the job is learning to delegate tasks and remembering you can't do everything yourself.