balloons, scissors, and a filler is all you need! We used birdseed (millet) this year, a change from the rice that was used at the Strawberry Music Festival (where we learned the craft). Now we don't have to worry much about the spillage!
Actually, there is another tool... a funnel made from the drinking end of a water bottle. We covered the cut edge with tape. It takes some practice to cram the birdseed down into the balloon, and some balloons are easier that others.