Frankly, the largest returns for my DS5 have been gained from activities that promote persistence, resilience, and prosocial thinking. These traits seem to be overlooked in school and many organized activities--or are only touched on tangentially.
Physical resilience builds a habit of mental resilience and, for that reason, I emphasize sports and time exploring in nature. Children need to learn to continually test their limits--and become comfortable with learning from failing-- if they are ever to achieve their potential.
For us recently, that looked like DS and me going on a long (for him) snowshoeing trek and having to push through the discomfort of continuing for the last kilometer. We took breaks as needed for his legs, and I carried him for stretches of about 100 meters at a time for a rest, but he did it! Other days, it could be us taking turns reading pages of a challenging but rewarding book, designing a wicked Lego structure from our own blueprints, or practicing parkour moves. Push the limit in activities with a strong intrinsic reward. It builds fabulous mental strength.
