Shopping - head off to the supermarket and grab everything you need. Remember that if the adults are staying, you may need to think about adult food. Most parents these days do not expect anything special but if you've got grandparents or elderly relatives coming, they usually like to eat something other than fairy bread with their cup of tea. If you're having the party in a local park or playground, contact a mobile coffee van and tell them where and when your party is so that they can turn up. That way, you'll keep the adults happy too - just pre-warn them to bring loose coins.