Prepare the snacks the night before the party; or better yet, take the day off from work and make the snacks that morning. OK, you CAN buy the snacks, but that's not nearly as much fun.
For nachos, use small, inexpensive ramekins so that children can dip their chips. Another salty favorite is, of course, pizza. Just realize that when you show up at your kid's school party with pizza, you are committed. Your child's friends will insist that you be the Room Mom or Dad forever!
A covered, plastic carrier is nice for cookies or cupcakes, but you can always use a foil-lined soft drink box.
Chill the drinks in an ice chest and you're ready to go to the party.
