Why not have a Chocolate Fest. Decorate with brown, black and white crepe paper and balloons and tell your guests to wear those colors.
Send chocolate kisses with the invitations or glue a piece of paper with the party details on the inside of a candy bar wrapper.
Serve everything chocolate including chocolate milk or cocoa, chocolate cake, lots of chocolate candy, chocolate ice cream. Make a chocolate dipping station with pretzels, fruit chunks (bananas, pineapple, strawberries), and anything else that sounds good.
Show the movie "Willy Wonka" or "Chocolat".
For games and activity ideas, take a look at my website, www.feelinfestive.com.