The Cake - if making the cake yourself, you can bake it and freeze it uncut.
Make up the Goody Bags for each child to take home with them and remember to make a couple of extras for younger siblings who might be at the party, although not officially on the guest list. Rather than filling the bags with lollies, you could do something different like follow the theme of the party: novelty items such as magic tricks, pencils with animals on top, porcelain fairies, stretchy animals, some simple painted shells with their names painted on will be treasures forever and won't break the bank. If the budget allows, think of giving something really different like a garden set, complete with kids' gloves, tools and seedlings, or a kids' cooking set with apron, cookbook and some biscuit cutters! Very stylish.