Measure the distance from your mouth to just below your knees.
Whatever number you measure, cut that much invisible thread off the spool. Invisible thread is a material magicians love because it CANNOT be seen even when looking right at it.
Spread out a dollar bill and lie the thread across it.
Tape the middle of the bill so the thread sticks.
Fold or crumple the dollar up so nobody can see the tape.
Place the end points of the thread in your mouth, like floss, and hit the streets.
Be dramatic. People cannot see invisible thread and will literally only see a weird guy walking around with money floating around him. Since the thread is in your mouth, you can show no string exists in your hands or sleeves.