Card games are very common at both math competitions and math/AI summer camps. I have discovered that other math and AI students are also huge enthusiasts for card games, board games, and brain teasers. Some games require cooperation, while others are individual; some require flexibility while others require efficiency. Name any obscure game and someone in a group of advanced STEM students will have played it. If you also love of card games, this can be a fun way to relax at STEM camps, events and competitions, and it is also a great ice breaker.
Some of your parents may think playing card games isn't the most productive way to spend time, but I think the opposite. There is extensive academic research linking the role of playing games to the development of core cognitive skills such as logical and strategic thinking, as well as problem solving. Playing a new card game is a chance to explore a new logical construct, and to take risks in exploring what winning strategies might be. I have played the card game SET for over a decade yet recently learned an entirely new and collaborative way to play while attending "Game Night" at Math Prize for Girls at MIT.
Here some of my favorite games (very loosely) grouped by age.