A word of caution, sometimes less is more when selecting themed partyware. If the tablecloth, plates, cups, and napkins all have the same design, it can be a bit overwhelming and hard to find items on the table. Buying a few items in coordinating solid colors will be more attractive and cost less.
Tie a cluster of balloons outside the party location to help guests find the party. Decorate the gift table and cake table with a balloon bouquet. When making balloon bouquets, use an odd number of balloons and space them at slightly different heights.
Weigh down helium-filled balloons with cans wrapped in gift wrap or foil or just also allow balloons to float up to the ceiling with long ribbons. Send a balloon home with each young party guest.
Call ahead or order helium balloons when you first enter the store and come back and get them after you've finished the rest of your shopping. It takes at least 10 minutes to fill a dozen balloons and this feels like a long time if you're just standing there watching. Helium-filled latex balloons (the regular colorful plastic ones) often fall after 12-24 hours, so pick them up the day of the party. However, if this isn't possible, ask the party store to put "high float" gel in the balloons. High float costs slightly more per balloon, but they'll float for 2 days, although the color and glossiness fades a bit after the 1st day. Freshly filled mylar balloons (the foil ones) will float for several days and don't require "high float".
Standard latex balloons are 11 inch diameter and these are fine for a children's party. However, if you're at party store that sells larger balloons (usually 17 inch diameter) and have a van or SUV to transport them, these larger balloons are very festive and don't cost much more. If you're transporting balloons in a regular-size car, one dozen 11 inch balloons is about the most you easily can fit. Anchor them down low in the back seat to keep from blocking your rear view mirror. You can rent or buy helium tanks and fill balloons yourself, but it's time consuming and doesn't save much money unless you have a lot of balloons to fill.
If you don't want to use helium balloons, just blow-up regular balloons and tie these to doorways or hang from the ceiling using curling ribbon and tape.
Party stores sell confetti in lots of fun shapes and colors. A couple sprinkles on the tables can add a festive look, but be careful around the food table or your guests will be eating it along with their cake. Instead, put some confetti, particularly if it's shaped to tie in with the theme (graduation caps for a Graduation Party), inside the party invitation. A fun little surprise and someone else has to clean it up!
Make a colorful welcome sign or a giant birthday card out of posterboard for guests to sign and add artwork to for a fun and personal keepsake.