Easiest Coin in Bottle by Fairmagic (Instant Download)

Show them an empty bottle (with or without contents) and borrow a coin.
Wrap this coin in some paper and place it on the lid of the bottle.
Take a lighter (can be borrowed) and light the paper. The coin visibly penetrates the lid of the bottle and lands inside the bottle. The bottle can be examined immediately and given away as a souvenir.