Concept
A blank deck of cards that acts as an inventory. In order for an object to be inserted in the card it must interact in a way with the cards.
Ideas
I take a pair of scissors and start cutting a card, only to see the scissor absorbed into the card and transformed into an illustration with a number and suit. I can later take this scissor out of the card.
If I punch a blank card, we can see an illustration of a punch appearing on the card. If it's a full deck of card you wanna insert in a card, you must spring it towards the card.
To produce something like a punch out of a card, you can make it comedic looking by having a full arm come out of the card and punch the individual in front of it.
Questions
How do you insert big objects inside of the card? A person, a car, a house?
How can you insert something object-specific, like two cars crashing, a person lifting an object?
How can you insert a thought or an emotion?
World
In another world, people have no more backpacks, no more luggage. Those who have understood how to take the potential of the blank deck to the highest highs are now seated in the highest positions.
For example, one might end up flying because she has inserted in the card a lot of compressed air and has figured out how to stock large quantities and release it fast and powerful.
Other people have sucked inside of their cards entire worlds and have ultimately committed deck suicide by allowing themselves to be sucked inside of that card. This idea can give birth to a whole corporation that revolves around the idea of allowing people to live young forever by creating Card Worlds where thousands of people have been sucked in and live in communion.
Potential: book, short story, sketch.
What if they would genetically make some bootleg versions and these could be used in the same way but would malfunction from time to time? Or these could be the ones you could use only 1 time whereas the ones you get when you are born can be used for forever.
I would also make it so chosen individuals, those who get Purple, Black, White Backed Cards can use their card in a special way, like @Vasile Bizau said regarding elements combining inside of the cards. This way you can have a Regular Card, a Bootleg one and The Special Ones - and boom, you have the beginning of a lore.
Everyone should also keep in mind that all of these stories can be used as patters for their magic performances. There's nothing better than a nice story to tell your audience, something that they can take with themselves back home and keep thinking about (besides the magic that you are performing).
The thing I am interested about is if you can combine elements inside of the blank cards. For example, if you add fire and wood, can you get ash? If you add paper and ink, can you get writing? And then take that element out of the card. It would be really useful, especially in survival situations.
I really like this Blank Card thing, but it might spin out of control if anyone is allowed to buy them or get them so easily. I suppose each individual is given a blank playing card when they are born and can sell it for a lot of cash to corporations who are buying them. Then you can motivate why some individuals have so many. There's also stealing and killing for the card.
1. I would say you'd spread a deck of cards on the ground nice and easy and a car would run them over, only to be absorbed into the last playing card. A person would most likely have to interact with the card a lot in order for her/him to be absorbed in it. I would see this happening to spectators who are being given a card as a souvenir. The magician who gave them the card could also track them somehow and once they've been absorbed in the card he would take them. You know, slowly build an army like this.
2. I'd make it so a card falls inbetween the cars in the moment of the crash, thus, absorbing the two and the action itself. I would see a company do something like this in order to create high end decks of cards which they could later sell to the army or some big corporations.
I think the better question would be, how long do these cards effect last? Is it a one use thing? Like Tyler Durdan and airplane "friends" ? The way I see it, once these cards have been labeled (two cars crashing, a punch, etc.) they can only holster that specific action from then on. Even if they become available after 1 use, you can only recharge them with the same action.
I'd love to see someone turn this into a card game somehow.