If I have my creative-generalist hat on and I am staring at a blank page without any initial idea of my creative direction I can use this technique to find a subject. I start with a directive in the format:
Name an X
then pick a random word to complete this directive:
Name a card.
From this point I can name as many cards as I can (perhaps setting a quota) or I can define/texture the directive with a random word. So with the random word 'water' used as an adjective my directive now reads:
Name a water card
This makes me think of:
Greetings cards with an astrological theme featuring the 'water' signs.
Plastic postcards of Tower Bridge that literally contain some Thames water.
The card shown by a water authority person to prove their identity.
The ESP card with a squiggly line.
All potentially interesting subjects for creativity.