Bring out a deck of Bicycle cards and remove it from its box. Spread the cards on the table as you ask, "Did anyone notice that I removed these cards from a tiny box?"
To everyone's surprise you are now holding a miniature Bicycle card box; the poker-sized box is completely gone!
Scoop up the deck as you explain, "There's no way this deck could fit inside that box - unless the cards were tiny, too."
Spread the cards on the table and now they too have shrunken to miniature Bicycle cards!
Remove a card from the spread and place it aside. Say, "I can change them back, but it happens quickly so watch closely."
Scoop up the deck and give it a shake - it grows back to poker size right before everyone's eyes!
Point to the miniature card that you placed aside and say, "Now for the last one..."
Wave your hand and it instantly expands to poker size!
At the conclusion you're left with an ordinary deck of cards to be used for your favorite card tricks!