Some wargaming rules (e.g. the charming
The Sword and the Flame) have what are known as action cards or event cards to randomly insert some unexpected happening into the game to spice things up. These are not CCGs per se, but might be a nice add-on to the game, as in chases, encounters, NPC reactions--the possibilities are nigh endless.
What I have engineered for my own gaming fun is a card-based system for (N)PC generation instead of dice rolls. I have a pack for combat-oriented skills, one for non-combat skills, one for blade combat, one for gun combat, and another for vehicle skills. In my campaign "blaster" (laser) arms are commonplace, so I intentionally boosted the weight for those skill cards, and so on. It is a very fun alternative to the same-old-same-old dice rolls.