The Deck of Cards is used for the gambling event and for gaining sanity. It takes up one slot during scavenging. There may be a military event which requires the player to use the card. It is sort of useful to survival in the fallout shelter, and as such should be considered as a medium priority.
Niagara Falls! Required: Map, Deck of Cards, Radio.
Summary: A flood occurs in the shelter and the player haves to choose from a Map, a Deck of Cards, or a Radio to save, but any items you didn't select become damaged. This event tends to happen very early, usually within the first two weeks. It is recommended to save the Radio, as it is needed for a winning ending; the Map is repairable with the Boy Scout Handbook, and the Deck of Cards isn't often needed for victory or many events.
The Gambler Required: Deck of Cards, at least 2 Water Bottles or 2 Soup Cans.
Summary: A stranger will ask to gamble with a deck of cards (they must be the player's own deck of cards). If the player loses, he/she lose 2 bottles of water/soup cans. If the player wins, he/she gains 2 bottles of water/soup cans. There is a 50/50 chance of success/loss (needs confirmation of 50/50 odds, may be unbalanced odds).
Noises From The Walls
The family will start hearing noises from the walls, and eventually they'll go crazy. The player haves the option to play with the Checkers or the Deck of Cards, but the Deck of Cards are much better, as the Checkers can leave a member with less sanity than before.
This item can also be traded for 2 water bottles from a traveling salesmen.