All the ways that playing cards can be used

Ways that I will use, and possibly perform in front of people:

• Playing multiplayer games, or solitaire / patience games. [wikipedia]
• Cardistry. ▶cardistry 101
• Card stacking / house of cards.
• Card throwing.
• Impossible bottles. ▶howto

Ways I might use the cards:

• Polyhedrals.
• Card magic / sleight of hand.
• Tearing a deck in half.
• An improvised bicycle noisemaker, a way to fix uneven table legs, or an impromptu toothpick.

Ways that I'm avoiding using the cards:

• Cheating. This could erode trust with close friends, so I plan to let others clearly know that I'm avoiding it completely.
• Cartomancy / fortune telling. I personally see this as pseudoscience, though I don't judge other people who like to do it.

Other gimmicks:

• business cards that look like a deck of playing cards — MakePlayingCards.com [2], PrintByMagic.com, Zazzle, TheGameCrafter.com, Kardwell, long list of more

References — [1] [2]