Clone Deck

• The magician shows the audience a plastic cardholder from which he removes a deck of cards. He snaps his fingers and suddenly there are TWO decks of cards in his hands. He opens one of the decks and pulls the cards from it, which he then uses to perform further tricks.
•  The magician shows a plastic cardholder to the audience from which he removes a deck of cards.
  Without opening the case and removing the cards, he spreads the cards out onto the table.
• The magician shows a red and a blue deck of cards to the audience. He asks "Which one do you chose? The red one or the blue?" The answer is "The blue one!" Ok, I'll just put the blue one to one side. 
  Now I'm left with two red decks!

Bonus routine:

A blue deck of card vanishing from the white case. Only one card remain in the case.

The blue deck of card appears beetween two red deck of cards under the silk.
From the blue deck one card is missing, which is actually in the white card case.