Caravan card

Caravan cards are miscellaneous items in Fallout: New Vegas.

Characteristics
Caravan cards are used to play the games Caravan and Blackjack. For Caravan, players use their own decks whereas casinos usually provide the cards deck for Blackjack. There are six sets of Caravan cards available: a standard deck, one for each of the casinos in New Vegas and one for the Sierra Madre Casino (with the add-on Dead Money.

Obtaining a Caravan card automatically adds it to the Caravan deck in the player's inventory.

Sierra Madre cards
Unlike the other cards, not all Sierra Madre cards can be found or purchased in the game world. In fact, they are not sold by merchants at all and only 21 can be found in the Sierra Madre and its surroundings.

Due to the fact that players do not have access to their caravan deck when in the Sierra Madre, the cards are initially not added to it and thus cannot be used when playing Caravan. Once back in the Mojave, placing the cards in a container (or simply dropping them) and picking them up again will make them available for regular use though.