The basic one cap routine is perfect. With minmal sleight of hand, you could vanish a coin easily.
Spectators see you to take out a bottle, and remove the cap. You put a coin into the cap,
and turn over. Spectators shake the cap, they could feel and hear the coin inside the cap. They use
their hand to cover the cap. You do some magical gesture. Then they shake the cap again, nothing.
They turn over the cap and find nothing inside. They examine the cap but find nothing. They could
never hear the coin again. The whole routine looks very impromptu, the gimmick looks like a real cap
from a water bottle. No spectator will supspect your cap is a gimmick.
However, the two
cap routine doesn't work well. Sometimes the coin may not appear as you wish. After the routine, if
the spectator examine the cap with the coin, they may find something abnormal. On the other hand,
it's not a good idea to bring out two bottles in front of spectators. I don't think someone will
take two water bottles at the same time. Spectators may suspect it.