Balloon, backing soda, vinegar, and a bottle.
Step 1: First step.
Take the balloon and fill it up with baking soda fill about half the balloon.
Step 2: Next.
Put vinegar about half way full in the bottle.
Step 3: Following.
Put the balloon over the lid of the water bottle and let the baking soda drop into the bottle.
Step 4: Lastly.
Watch the balloon fill up with co2.