Invisible Hole
A wonderful version of a great old classic. Two clear tubes are fitted neatly together with an ordinary playing card in between. Everything can be examined and the spectator could even assemble the whole thing themselves.
Four coins (20 cent pieces are perfect and these could be borrowed) are dropped in to the tube and, one a time, they visually penetrate the card.
As a kicker you offer to explain how the effect works and turn the tube upside down over the spectator's hand and out drops a huge, real battery. See, its electronic! Beautifully hand crafted for us in Germany.