Other business card thoughts include:

Thermochromic ink that reveals a URL to a puzzle site that opens my work-in-progress playground.

Conductive ink that allows the holder to light up an LED embedded in the card with their fingers (yet to be seen if possible).

A paper USB drive that contains examples of my work and a thank-you piece.

More NFC.

A PCB of some sort as the card itself.

Some sort of short executable code to use on my website to access secrets.

A sort of holographic glitchy effect.