Imagine taking a deck of cards out of the card case, you show the card case empty, then upon placing the deck of cards on the table and spreading it, except for one card the rest of the deck returns inside the card case.
Method Idea
Has to be some kind of flap gimmick that makes it look as if you took the entirety of the deck out of the case then another flap thingy that shows the card case to be empty when you turn it towards the spectators.
What do you think?
Sketch
Timma is performing on stage the previously described effect. The crowd is heard clapping at the reveal of the deck having returned almost entirely back inside the card case.
Timma takes the deck out of the card case again, in order to perform a follow-up effect, but finds that as soon as she spreads the deck for a spectator to choose a card, the cards have went back inside the card case.
She might give it a few more tries and ultimately asks for somebody to hand her a deck of cards. Someone does, and when she gets the cards out of the case, all vanish except for a single card. When she looks back at the original card case, it has doubled in size.
She now gives up completely trying to use a deck of cards and instead asks for some coins. Someone gives her a bunch of coins. She takes them in her hand and as she places them on the table, all vanish instead of one.
She then asks for someone's wallet. Everything from inside vanishes except for the wallet.
She then asks for a spectator to help her by coming on stage - the spectator vanishes except for a pair of boxer-shorts.
Upon looking at the original card case, it has become the size of a wardrobe, clearly having stored everything that has vanished up until then.