Hi Leon!
You are definitely in for a holly, jolly good time! Not only will you be visiting Walt Disney World during the most magical time of the year, but
Mickey's Very Merry Christmas Party is an extra fun way to celebrate the season with your family.
I attended the Party last year and loved every single second, from seeing the snow fall on Main Street, U.S.A. to watching Santa and his Disney friends float by in Mickey's Once Upon a Christmastime Parade. And let's not forget about those treats! Complimentary cookies and hot cocoa are included with your Party ticket. Last year, there were 7 locations around Magic Kingdom to pick up those snacks, which meant you could keep your tummy full all night. For Guests with special dietary needs, there were also some alternate options that were available upon request - apple slices, apple juice, vegan chocolate chip cookies and sugar-free hot cocoa. I don't recall seeing coffee offered at any of those treat spots (although things can always change from one year to the next), you can always stop by one of the open dining locations to purchase some, including the Starbucks in the Main Street Bakery.
Be sure to pick up a Party Guide when you enter the park for information on all the merriment, including the locations and hours of those treat locations. I hope that helps, Leon, but please stop back by with any other questions you have as you make your plans.
Beth